Affine linear weighted intra prediction in video coding

ABSTRACT

A video coder performs a Most-Probable Mode (MPM) derivation process that derives one or more MPMs for a current block that is not coded using affine linear weighted intra prediction (ALWIP). As part of performing the MPM derivation process, the video coder determines whether a neighboring block of the current block is an ALWIP-coded neighboring block. Based on the neighboring block being an ALWIP-coded neighboring block, the video coder determines that a value of an intra prediction mode of the neighboring block is a value indicating a planar mode. The video coder codes the current block based on one of the MPMs for the current block.

This application claims the benefit of U.S. Provisional PatentApplication 62/845,790, filed May 9, 2019, and U.S. Provisional PatentApplication 62/864,320, filed Jun. 20, 2019, the entire content of eachof which is incorporated by reference.

TECHNICAL FIELD

This disclosure relates to video encoding and video decoding.

BACKGROUND

Digital video capabilities can be incorporated into a wide range ofdevices, including digital televisions, digital direct broadcastsystems, wireless broadcast systems, personal digital assistants (PDAs),laptop or desktop computers, tablet computers, e-book readers, digitalcameras, digital recording devices, digital media players, video gamingdevices, video game consoles, cellular or satellite radio telephones,so-called “smart phones,” video teleconferencing devices, videostreaming devices, and the like. Digital video devices implement videocoding techniques, such as those described in the standards defined byMPEG-2, MPEG-4, ITU-T H.263, ITU-T H.264/MPEG-4, Part 10, Advanced VideoCoding (AVC), ITU-T H.265/High Efficiency Video Coding (HEVC), andextensions of such standards. The video devices may transmit, receive,encode, decode, and/or store digital video information more efficientlyby implementing such video coding techniques.

Video coding techniques include spatial (intra-picture) predictionand/or temporal (inter-picture) prediction to reduce or removeredundancy inherent in video sequences. For block-based video coding, avideo slice (e.g., a video picture or a portion of a video picture) maybe partitioned into video blocks, which may also be referred to ascoding tree units (CTUs), coding units (CUs) and/or coding nodes. Videoblocks in an intra-coded (I) slice of a picture are encoded usingspatial prediction with respect to reference samples in neighboringblocks in the same picture. Video blocks in an inter-coded (P or B)slice of a picture may use spatial prediction with respect to referencesamples in neighboring blocks in the same picture or temporal predictionwith respect to reference samples in other reference pictures. Picturesmay be referred to as frames, and reference pictures may be referred toas reference frames.

SUMMARY

In general, this disclosure describes techniques for intra prediction,including the derivation and signaling of modes for linear weightedintra prediction. For instance, in one example, this disclosuredescribes a video coder, such as a video encoder or a video decoder,that performs a Most-Probable Mode (MPM) derivation process that derivesone or more MPMs for a current block that is not coded using affinelinear weighted intra prediction (ALWIP). The MPMs for the current blockmay be intra prediction modes determined to be most likely to be usedfor coding the current block. As part of performing the MPM derivationprocess, the video coder determines whether a neighboring block of thecurrent block is an ALWIP-coded neighboring block. Based on theneighboring block being an ALWIP-coded neighboring block, the videocoder determines that a value of an intra prediction mode of theneighboring block is a default value, such as a value corresponding to aplanar mode. The video coder codes the current block based on one of theMPMs for the current block.

In one example, this disclosure describes a method of coding video data,the method comprising: performing a Most-Probable Mode (MPM) derivationprocess that derives one or more MPMs for a current block of the videodata, wherein the current block is not coded using affine linearweighted intra prediction (ALWIP), and performing the MPM derivationprocess comprises: determining whether a neighboring block of thecurrent block is an ALWIP-coded neighboring block; and based on theneighboring block being an ALWIP-coded neighboring block: determiningthat a value of an intra prediction mode of the neighboring block is adefault value; and including an intra prediction mode corresponding tothe default value as one of the one or more MPMs, and coding the currentblock based on one of the MPMs for the current block.

In another example, this disclosure describes a device for coding videodata, the device comprising: a memory to store the video data; and oneor more processors implemented in circuitry, the one or more processorsconfigured to: perform a Most-Probable Mode (MPM) derivation processthat derives one or more MPMs for a current block of the video data,wherein the current block is not coded using affine linear weightedintra prediction (ALWIP), and performing the MPM derivation processcomprises: determine whether a neighboring block of the current block isan ALWIP-coded neighboring block; and based on the neighboring blockbeing an ALWIP-coded neighboring block: determine that a value of anintra prediction mode of the neighboring block is a default value; andinclude an intra prediction mode corresponding to the default values asone of the one or more MPMs; and code the current block based on one ofthe MPMs for the current block.

In another example, this disclosure describes a device for coding videodata, the device comprising: means for performing a Most-Probable Mode(MPM) derivation process that derives one or more MPMs for a currentblock of the video data, wherein the current block is not coded usingaffine linear weighted intra prediction (ALWIP), and the means forperforming the MPM derivation process comprises: means for determiningwhether a neighboring block of the current block is an ALWIP-codedneighboring block; and means for determining, based on the neighboringblock being an ALWIP-coded neighboring block, that a value of an intraprediction mode of the neighboring block is a default value andincluding an intra prediction mode corresponding to the default value asone of the one or more MPMs; and means for coding the current blockbased on one of the MPMs for the current block.

In another example, this disclosure describes a computer-readablestorage medium having stored thereon instructions that, when executed,cause one or more processors to: perform a Most-Probable Mode (MPM)derivation process that derives one or more MPMs for a current block ofvideo data, wherein the current block is not coded using affine linearweighted intra prediction (ALWIP), and performing the MPM derivationprocess comprises: determine whether a neighboring block of the currentblock is an ALWIP-coded neighboring block; and based on the neighboringblock being an ALWIP-coded neighboring block: determine that a value ofan intra prediction mode of the neighboring block is a default value;and include an intra prediction mode corresponding to the default valueas one of the one or more MPMs; and code the current block based on oneof the MPMs for the current block.

The details of one or more examples are set forth in the accompanyingdrawings and the description below. Other features, objects, andadvantages will be apparent from the description, drawings, and claims.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a block diagram illustrating an example video encoding anddecoding system that may perform the techniques of this disclosure.

FIG. 2 is a block diagram illustrating an example of intra prediction,with arrows pointing toward reference samples.

FIG. 3 is a conceptual diagram of an example of 8×4 rectangular blockwhere “closer” reference samples are not used, but farther referencesamples may be used due to a restriction of an intra predictiondirection to be in the range of −135 degrees to 45 degrees.

FIG. 4 is a conceptual diagram illustrating wide angles (−1 to −10, and67 to 76) depicted in addition to the 65 angular modes.

FIGS. 5A, 5B, and 5C are illustrations of mode mapping processes forintra prediction modes outside a diagonal direction range.

FIG. 6 is a conceptual diagram illustrating wide angles (−1 to −14, and67 to 80) in VVC Test Model 3 (VTM3) beyond modes 2 and 66 for a totalof 93 angular modes.

FIG. 7 is a table providing a specification of intra prediction angles.

FIG. 8 is an illustration of reference samples from multiple referencelines that may be used for intra prediction of the coding block.

FIG. 9 is a conceptual diagram illustrating an example of division of4×8 and 8×4 blocks.

FIG. 10 is a conceptual diagram illustrating an example of division ofall blocks except 4×8, 8×4, and 4×4.

FIG. 11 is a conceptual diagram illustrating an example of an affinelinear weighted intra prediction (ALWIP) process on 8×8 block.

FIG. 12 is a table illustrating the number of matrix parameters andoffset parameters for each ALWIP type in Versatile Video Coding WorkingDraft 4 (VVC WD4).

FIG. 13 is a conceptual diagram illustrating example neighboring blocksused to derive ALWIP most probable modes (MPMs) for a current block, inaccordance with one or more techniques of this disclosure.

FIGS. 14A and 14B are conceptual diagrams illustrating an examplequadtree binary tree (QTBT) structure, and a corresponding coding treeunit (CTU).

FIG. 15 is a block diagram illustrating an example video encoder thatmay perform the techniques of this disclosure.

FIG. 16 is a block diagram illustrating an example video decoder thatmay perform the techniques of this disclosure.

FIG. 17 is a flowchart illustrating an example method for encoding acurrent block.

FIG. 18 is a flowchart illustrating an example method for decoding acurrent block of video data.

FIG. 19 is a flowchart illustrating an example method of coding videodata, in accordance with one or more techniques of this disclosure.

FIG. 20 is a flowchart illustrating an example method of coding a chromablock, in accordance with one or more techniques of this disclosure.

DETAILED DESCRIPTION

Affine linear weighted intra prediction (ALWIP) is a form of intraprediction in which a prediction block is generated by down-samplingreference samples of a block, multiplying a vector of the down-sampledreference samples by a matrix and adding a bias vector, mapping theresulting sample values into predetermined positions within theprediction block, and performing linear interpolation on the samplevalues in the prediction block to determine sample values for theremaining positions within the prediction block. The use of ALWIP maylead to better coding efficiencies for some types of blocks, but regularintra prediction techniques may lead to better coding efficiencies thanALWIP for other types of blocks. Thus, some blocks within a picture maybe coded using ALWIP and some blocks within a picture may be coded usingregular intra prediction techniques, such as a planar intra predictionmode, a DC intra prediction mode, or a directional intra predictionmode. Although the above example describes several steps for ALWIP, someimplementations may choose to exclude one or more of the above steps,and other implementations may include other steps to the derivationprocess. However, a core idea in ALWIP is multiplying a vector ofsamples derived from reference samples with a matrix (or equivalentoperation).

To improve the efficiency of signaling an intra prediction mode (e.g., aplanar, DC, or directional intra prediction mode), a video coder (e.g.,a video encoder or a video decoder) may perform a most-probable mode(MPM) derivation process that derives one or more MPMs for a currentblock of video data. Each of the MPMs may be an intra prediction mode.If the optimal intra prediction mode for the current block is one of theMPMs, an index indicating one of the MPMs may be signaled in abitstream. If the optimal intra prediction mode for the current block isnot one of the MPMs, an index indicating one of the non-MPM intraprediction modes may be signaled. Because there are fewer MPMs thanthere are non-MPM intra prediction modes, an index indicating an MPMsmay be coded using significantly fewer bits than an index indicating oneof the non-MPM intra prediction modes. Thus, the use of the MPMderivation process may increase coding efficiency for some blocks.

The video coder may derive the MPMs based on the intra prediction modesof blocks that neighbor the current block. For instance, if a leftneighboring block is coded using a DC intra prediction mode, the videocoder may determine that one of the MPMs is the DC intra predictionmode. However, in the MPM derivation process, if one of the neighboringblocks is coded using ALWIP, the video coder performs a process thatuses mapping data that maps ALWIP parameters of the neighboring block toone of the directional intra prediction modes. The ALWIP parametersinclude matrix coefficients and a bias vector. The video coder may thenuse the determined directional intra prediction mode as one of the MPMs.

Storing the mapping data increases the data storage requirements ofvideo encoders and video decoders. The increased data storagerequirements may increase the cost and complexity of video encoders andvideo decoders. Moreover, the lookup operations that are performed touse the mapping data take time, which may slow down the encoding anddecoding processes. Additionally, a prediction block generated using anintra prediction mode determined using the mapping data is only anapproximation of the prediction block that would be generated if theALWIP parameters of the neighboring block were used. This approximationmay decrease coding efficiency.

The techniques of this disclosure may address one or more of theseissues. For instance, as described in an example of this disclosure, avideo coder (e.g., a video encoder or a video decoder) may perform anMPM derivation process that derives one or more MPMs for a current blockof the video data. In this example, the current block is not coded usingALWIP. As part of performing the MPM derivation process, the video codermay determine whether a neighboring block of the current block is anALWIP-coded neighboring block. Based on the neighboring block being anALWIP-coded neighboring block, the video coder may determine that avalue of an intra prediction mode of the neighboring block is a defaultvalue, such as a value corresponding to a planar mode. Accordingly, thevideo coder may include an intra prediction mode corresponding to thedefault value as one of the MPMs. The video coder may code the currentblock based on one of the MPMs for the current block.

By using the intra prediction mode corresponding to the default value asone of the MPMs when the neighboring block is ALWIP-coded, the videocoder may avoid the need to store the mapping data. Avoiding the need tostore the mapping data may reduce the data storage requirements of thevideo coder, which may reduce the cost and complexity of the videocoder. Furthermore, avoiding use of the mapping data may accelerate theencoding and decoding processes by avoiding the lookup operationsinvolved with use of the mapping data.

FIG. 1 is a block diagram illustrating an example video encoding anddecoding system 100 that may perform the techniques of this disclosure.The techniques of this disclosure are generally directed to coding(encoding and/or decoding) video data. In general, video data includesany data for processing a video. Thus, video data may include raw,unencoded video, encoded video, decoded (e.g., reconstructed) video, andvideo metadata, such as signaling data.

As shown in FIG. 1, system 100 includes a source device 102 thatprovides encoded video data to be decoded and displayed by a destinationdevice 116, in this example. In particular, source device 102 providesthe video data to destination device 116 via a computer-readable medium110. Source device 102 and destination device 116 may include any of awide range of devices, including desktop computers, notebook (i.e.,laptop) computers, set-top boxes, mobile devices such as telephonehandsets (e.g., smartphones) and tablet computers, televisions, cameras,display devices, digital media players, video gaming consoles, videostreaming device, a broadcast receiver device, or the like. In somecases, source device 102 and destination device 116 may be equipped forwireless communication, and thus may be referred to as wirelesscommunication devices.

In the example of FIG. 1, source device 102 includes video source 104,memory 106, video encoder 200, and output interface 108. Destinationdevice 116 includes input interface 122, video decoder 300, memory 120,and display device 118. In accordance with this disclosure, videoencoder 200 of source device 102 and video decoder 300 of destinationdevice 116 may be configured to apply the techniques for performingintra prediction, including the derivation and signaling of modes forlinear weighted intra prediction. Thus, source device 102 represents anexample of a video encoding device, while destination device 116represents an example of a video decoding device. In other examples, asource device and a destination device may include other components orarrangements. For example, source device 102 may receive video data froman external video source, such as an external camera. Likewise,destination device 116 may interface with an external display device,rather than including an integrated display device.

System 100 as shown in FIG. 1 is merely one example. In general, anydigital video encoding and/or decoding device may perform techniques forperforming intra prediction, including the derivation and signaling ofmodes for linear weighted intra prediction. Source device 102 anddestination device 116 are merely examples of such coding devices inwhich source device 102 generates encoded video data for transmission todestination device 116. This disclosure refers to a “coding” device as adevice that performs coding (encoding and/or decoding) of data. Thus,video encoder 200 and video decoder 300 represent examples of codingdevices, in particular, a video encoder and a video decoder,respectively. In some examples, source device 102 and destination device116 may operate in a substantially symmetrical manner such that each ofsource device 102 and destination device 116 include video encoding anddecoding components. Hence, system 100 may support one-way or two-wayvideo transmission between source device 102 and destination device 116,e.g., for video streaming, video playback, video broadcasting, or videotelephony.

In general, video source 104 represents a source of video data (i.e.,raw, unencoded video data) and provides a sequential series of pictures(also referred to as “frames”) of the video data to video encoder 200,which encodes data for the pictures. Video source 104 of source device102 may include a video capture device, such as a video camera, a videoarchive containing previously captured raw video, and/or a video feedinterface to receive video from a video content provider. As a furtheralternative, video source 104 may generate computer graphics-based dataas the source video, or a combination of live video, archived video, andcomputer-generated video. In each case, video encoder 200 encodes thecaptured, pre-captured, or computer-generated video data. Video encoder200 may rearrange the pictures from the received order (sometimesreferred to as “display order”) into a coding order for coding. Videoencoder 200 may generate a bitstream including encoded video data.Source device 102 may then output the encoded video data via outputinterface 108 onto computer-readable medium 110 for reception and/orretrieval by, e.g., input interface 122 of destination device 116.

Memory 106 of source device 102 and memory 120 of destination device 116represent general purpose memories. In some example, memories 106, 120may store raw video data, e.g., raw video from video source 104 and raw,decoded video data from video decoder 300. Additionally oralternatively, memories 106, 120 may store software instructionsexecutable by, e.g., video encoder 200 and video decoder 300,respectively. Although memory 106 and memory 120 are shown separatelyfrom video encoder 200 and video decoder 300 in this example, it shouldbe understood that video encoder 200 and video decoder 300 may alsoinclude internal memories for functionally similar or equivalentpurposes. Furthermore, memories 106, 120 may store encoded video data,e.g., output from video encoder 200 and input to video decoder 300. Insome examples, portions of memories 106, 120 may be allocated as one ormore video buffers, e.g., to store raw, decoded, and/or encoded videodata.

Computer-readable medium 110 may represent any type of medium or devicecapable of transporting the encoded video data from source device 102 todestination device 116. In one example, computer-readable medium 110represents a communication medium to enable source device 102 totransmit encoded video data directly to destination device 116 inreal-time, e.g., via a radio frequency network or computer-basednetwork. Output interface 108 may modulate a transmission signalincluding the encoded video data, and input interface 122 may demodulatethe received transmission signal, according to a communication standard,such as a wireless communication protocol. The communication medium mayinclude any wireless or wired communication medium, such as a radiofrequency (RF) spectrum or one or more physical transmission lines. Thecommunication medium may form part of a packet-based network, such as alocal area network, a wide-area network, or a global network such as theInternet. The communication medium may include routers, switches, basestations, or any other equipment that may be useful to facilitatecommunication from source device 102 to destination device 116.

In some examples, computer-readable medium 110 may include storagedevice 112. Source device 102 may output encoded data from outputinterface 108 to storage device 112. Similarly, destination device 116may access encoded data from storage device 112 via input interface 122.Storage device 112 may include any of a variety of distributed orlocally accessed data storage media such as a hard drive, Blu-ray discs,DVDs, CD-ROMs, flash memory, volatile or non-volatile memory, or anyother suitable digital storage media for storing encoded video data.

In some examples, computer-readable medium 110 may include file server114 or another intermediate storage device that may store the encodedvideo data generated by source device 102. Source device 102 may outputencoded video data to file server 114 or another intermediate storagedevice that may store the encoded video generated by source device 102.Destination device 116 may access stored video data from file server 114via streaming or download. File server 114 may be any type of serverdevice capable of storing encoded video data and transmitting thatencoded video data to the destination device 116. File server 114 mayrepresent a web server (e.g., for a website), a File Transfer Protocol(FTP) server, a content delivery network device, or a network attachedstorage (NAS) device. Destination device 116 may access encoded videodata from file server 114 through any standard data connection,including an Internet connection. This may include a wireless channel(e.g., a Wi-Fi connection), a wired connection (e.g., digital subscriberline (DSL), cable modem, etc.), or a combination of both that issuitable for accessing encoded video data stored on file server 114.File server 114 and input interface 122 may be configured to operateaccording to a streaming transmission protocol, a download transmissionprotocol, or a combination thereof.

Output interface 108 and input interface 122 may represent wirelesstransmitters/receiver, modems, wired networking components (e.g.,Ethernet cards), wireless communication components that operateaccording to any of a variety of IEEE 802.11 standards, or otherphysical components. In examples where output interface 108 and inputinterface 122 include wireless components, output interface 108 andinput interface 122 may be configured to transfer data, such as encodedvideo data, according to a cellular communication standard, such as 4G,4G-LTE (Long-Term Evolution), LTE Advanced, 5G, or the like. In someexamples where output interface 108 includes a wireless transmitter,output interface 108 and input interface 122 may be configured totransfer data, such as encoded video data, according to other wirelessstandards, such as an IEEE 802.11 specification, an IEEE 802.15specification (e.g., ZigBee™), a Bluetooth™ standard, or the like. Insome examples, source device 102 and/or destination device 116 mayinclude respective system-on-a-chip (SoC) devices. For example, sourcedevice 102 may include an SoC device to perform the functionalityattributed to video encoder 200 and/or output interface 108, anddestination device 116 may include an SoC device to perform thefunctionality attributed to video decoder 300 and/or input interface122.

The techniques of this disclosure may be applied to video coding insupport of any of a variety of multimedia applications, such asover-the-air television broadcasts, cable television transmissions,satellite television transmissions, Internet streaming videotransmissions, such as dynamic adaptive streaming over HTTP (DASH),digital video that is encoded onto a data storage medium, decoding ofdigital video stored on a data storage medium, or other applications.

Input interface 122 of destination device 116 receives an encoded videobitstream from computer-readable medium 110 (e.g., a communicationmedium, storage device 112, file server 114, or the like). The encodedvideo bitstream may include signaling information defined by videoencoder 200, which is also used by video decoder 300, such as syntaxelements having values that describe characteristics and/or processingof video blocks or other coded units (e.g., slices, pictures, groups ofpictures, sequences, or the like). Display device 118 displays decodedpictures of the decoded video data to a user. Display device 118 mayrepresent any of a variety of display devices such as a cathode ray tube(CRT), a liquid crystal display (LCD), a plasma display, an organiclight emitting diode (OLED) display, or another type of display device.

Although not shown in FIG. 1, in some examples, video encoder 200 andvideo decoder 300 may each be integrated with an audio encoder and/oraudio decoder, and may include appropriate MUX-DEMUX units, or otherhardware and/or software, to handle multiplexed streams including bothaudio and video in a common data stream. If applicable, MUX-DEMUX unitsmay conform to the ITU H.223 multiplexer protocol, or other protocolssuch as the user datagram protocol (UDP).

Video encoder 200 and video decoder 300 each may be implemented as anyof a variety of suitable encoder and/or decoder circuitry, such as oneor more microprocessors, digital signal processors (DSPs), applicationspecific integrated circuits (ASICs), field programmable gate arrays(FPGAs), discrete logic, software, hardware, firmware or anycombinations thereof. When the techniques are implemented partially insoftware, a device may store instructions for the software in asuitable, non-transitory computer-readable medium and execute theinstructions in hardware using one or more processors to perform thetechniques of this disclosure. Each of video encoder 200 and videodecoder 300 may be included in one or more encoders or decoders, eitherof which may be integrated as part of a combined encoder/decoder (CODEC)in a respective device. A device including video encoder 200 and/orvideo decoder 300 may include an integrated circuit, a microprocessor,and/or a wireless communication device, such as a cellular telephone.

Video encoder 200 and video decoder 300 may operate according to a videocoding standard, such as ITU-T H.265, also referred to as HighEfficiency Video Coding (HEVC) or extensions thereto, such as themulti-view and/or scalable video coding extensions. Alternatively, videoencoder 200 and video decoder 300 may operate according to otherproprietary or industry standards, such as the Joint Exploration TestModel (JEM) or ITU-T H.266, also referred to as Versatile Video Coding(VVC). A draft of the VVC standard is described in Bross, et al.“Versatile Video Coding (Draft 4),” Joint Video Experts Team (JVET) ofITU-T SG 16 WP 3 and ISO/IEC JTC 1/SC 29/WG 11, 13^(th) Meeting:Marrakech, MA, 9-18 Jan. 2019, JVET-M1001 (hereinafter “VVC WD4”).Another draft of the VVC standard is described in Bross, et al.“Versatile Video Coding (Draft 5),” Joint Video Experts Team (JVET) ofITU-T SG 16 WP 3 and ISO/IEC JTC 1/SC 29/WG 11, 14^(th) Meeting: Geneva,CH, 19-27 Mar. 2019, JVET-N1001-v5 (hereinafter “VVC Draft 5”). Anobjective of VVC is to provide a significant improvement in compressionperformance over the existing HEVC standard, aiding in deployment ofhigher-quality video services and emerging applications such as 360°omnidirectional immersive multimedia and high-dynamic-range (HDR) video.The techniques of this disclosure, however, are not limited to anyparticular coding standard.

In general, video encoder 200 and video decoder 300 may performblock-based coding of pictures. The term “block” generally refers to astructure including data to be processed (e.g., encoded, decoded, orotherwise used in the encoding and/or decoding process). For example, ablock may include a two-dimensional matrix of samples of luminanceand/or chrominance data. In general, video encoder 200 and video decoder300 may code video data represented in a YUV (e.g., Y, Cb, Cr) format.That is, rather than coding red, green, and blue (RGB) data for samplesof a picture, video encoder 200 and video decoder 300 may code luminanceand chrominance components, where the chrominance components may includeboth red hue and blue hue chrominance components. In some examples,video encoder 200 converts received RGB formatted data to a YUVrepresentation prior to encoding, and video decoder 300 converts the YUVrepresentation to the RGB format. Alternatively, pre- andpost-processing units (not shown) may perform these conversions.

This disclosure may generally refer to coding (e.g., encoding anddecoding) of pictures to include the process of encoding or decodingdata of the picture. Similarly, this disclosure may refer to coding ofblocks of a picture to include the process of encoding or decoding datafor the blocks, e.g., prediction and/or residual coding. An encodedvideo bitstream generally includes a series of values for syntaxelements representative of coding decisions (e.g., coding modes) andpartitioning of pictures into blocks. Thus, references to coding apicture or a block should generally be understood as coding values forsyntax elements forming the picture or block.

HEVC defines various blocks, including coding units (CUs), predictionunits (PUs), and transform units (TUs). According to HEVC, a video coder(such as video encoder 200) partitions a coding tree unit (CTU) into CUsaccording to a quadtree structure. That is, the video coder partitionsCTUs and CUs into four equal, non-overlapping squares, and each node ofthe quadtree has either zero or four child nodes. Nodes without childnodes may be referred to as “leaf nodes,” and CUs of such leaf nodes mayinclude one or more PUs and/or one or more TUs. The video coder mayfurther partition PUs and TUs. For example, in HEVC, a residual quadtree(RQT) represents partitioning of TUs. In HEVC, PUs represent interprediction data, while TUs represent residual data. CUs that are intrapredicted include intra prediction information, such as an intraprediction mode indication.

As another example, video encoder 200 and video decoder 300 may beconfigured to operate according to JEM or VVC. According to JEM or VVC,a video coder (such as video encoder 200) partitions a picture into aplurality of CTUs. Video encoder 200 may partition a CTU according to atree structure, such as a quadtree-binary tree (QTBT) structure orMulti-Type Tree (MTT) structure. The QTBT structure removes the conceptsof multiple partition types, such as the separation between CUs, PUs,and TUs of HEVC. A QTBT structure includes two levels: a first levelpartitioned according to quadtree partitioning, and a second levelpartitioned according to binary tree partitioning. A root node of theQTBT structure corresponds to a CTU. Leaf nodes of the binary treescorrespond to coding units (CUs).

In an MTT partitioning structure, blocks may be partitioned using aquadtree (QT) partition, a binary tree (BT) partition, and one or moretypes of triple tree (TT) partitions. A triple tree partition is apartition where a block is split into three sub-blocks. In someexamples, a triple tree partition divides a block into three sub-blockswithout dividing the original block through the center. The partitioningtypes in MTT (e.g., QT, BT, and TT), may be symmetrical or asymmetrical.

In some examples, video encoder 200 and video decoder 300 may use asingle QTBT or MTT structure to represent each of the luminance andchrominance components, while in other examples, video encoder 200 andvideo decoder 300 may use two or more QTBT or MTT structures, such asone QTBT/MTT structure for the luminance component and another QTBT/MTTstructure for both chrominance components (or two QTBT/MTT structuresfor respective chrominance components).

Video encoder 200 and video decoder 300 may be configured to usequadtree partitioning, QTBT partitioning, MTT partitioning, or otherpartitioning structures. For purposes of explanation, the description ofthe techniques of this disclosure is presented with respect to QTBTpartitioning. However, it should be understood that the techniques ofthis disclosure may also be applied to video coders configured to usequadtree partitioning, or other types of partitioning as well.

This disclosure may use “N×N” and “N by N” interchangeably to refer tothe sample dimensions of a block (such as a CU or other video block) interms of vertical and horizontal dimensions, e.g., 16×16 samples or 16by 16 samples. In general, a 16×16 CU has 16 samples in a verticaldirection (y=16) and 16 samples in a horizontal direction (x=16).Likewise, an N×N CU has N samples in a vertical direction and N samplesin a horizontal direction, where N represents a nonnegative integervalue. The samples in a CU may be arranged in rows and columns.Moreover, CUs need not necessarily have the same number of samples inthe horizontal direction as in the vertical direction. For example, CUsmay include N×M samples, where M is not necessarily equal to N.

Video encoder 200 encodes video data for CUs representing predictionand/or residual information, and other information. The predictioninformation indicates how the CU is to be predicted in order to form aprediction block for the CU. The residual information generallyrepresents sample-by-sample differences between samples of the CU priorto encoding and the prediction block.

To predict a CU, video encoder 200 may generally form a prediction blockfor the CU through inter prediction or intra prediction. Interprediction generally refers to predicting the CU from data of one ormore previously coded pictures, whereas intra prediction generallyrefers to predicting the CU from previously coded data of the samepicture. To perform inter prediction, video encoder 200 may generate theprediction block using one or more motion vectors. Video encoder 200 maygenerally perform a motion search to identify a reference block thatclosely matches the CU, e.g., in terms of differences between the CU andthe reference block. Video encoder 200 may calculate a difference metricusing a sum of absolute difference (SAD), sum of squared differences(SSD), mean absolute difference (MAD), mean squared differences (MSD),or other such difference calculations to determine whether a referenceblock closely matches the current CU. In some examples, video encoder200 may predict the current CU using uni-directional prediction orbi-directional prediction.

Some examples of JEM and VVC also provide an affine motion compensationmode, which may be considered an inter prediction mode. In affine motioncompensation mode, video encoder 200 may determine two or more motionvectors that represent non-translational motion, such as zoom in or out,rotation, perspective motion, or other irregular motion types.

To perform intra prediction, video encoder 200 may select an intraprediction mode to generate the prediction block. Some examples of JEMand VVC provide sixty-seven intra prediction modes, including variousdirectional modes, as well as a planar mode and a DC mode. In general,video encoder 200 selects an intra prediction mode that describesneighboring samples to a current block (e.g., a block of a CU) fromwhich to predict samples of the current block. Such samples maygenerally be above, above and to the left, or to the left of the currentblock in the same picture as the current block, assuming video encoder200 codes CTUs and CUs in raster scan order (left to right, top tobottom).

In general, a video coder, such as video encoder 200 or video decoder300, may generate a prediction block using planar mode as a gradientestimated from neighboring samples. For instance, in VVC WD4, a videocoder may generate a prediction block using the planar intra predictionmode as follows.

8.3.4.2.5 Specification of INTRA_PLANAR Intra Prediction Mode

Inputs to this process are:

-   -   a variable nTbW specifying the transform block width,    -   a variable nTbH specifying the transform block height,    -   the neighbouring samples p[x][y], with x=−1, y=−1 . . . nTbH and        x=0 . . . nTbW, y=−1.

Outputs of this process are the predicted samples predSamples[x][y],with x=0 . . . nTbW−1, y=0 . . . nTbH−1.

The variables nW and nH are derived as follows:nW=Max(nTbW,2)  (8-115)nH=Max(nTbH,2)  (8-116)

The values of the prediction samples predSamples[x][y], with x=0 . . .nTbW−1 and y=0 . . . nTbH−1, are derived as follows:predV[x][y]=((nH−1−y)*p[x][−1]+(y+1)*p[−1][nTbH])<<Log 2(nW)  8-117)predH[ x][ y]=((nW−1−x)*p[−1][ y]+(x+1)*p[nTbW][−1])<<Log 2(nH)  (8-118)predSamples[x][y]=(predV[x][y]+predH[x][y]+nW*nH)>>(Log 2(nW)+Log2(nH)+1)  (8-119)

Video encoder 200 encodes data representing the prediction mode for acurrent block. For example, for inter prediction modes, video encoder200 may encode data representing which of the various availableinter-prediction modes is used, as well as motion information for thecorresponding mode. For uni-directional or bi-directional interprediction, for example, video encoder 200 may encode motion vectorsusing advanced motion vector prediction (AMVP) or merge mode. Videoencoder 200 may use similar modes to encode motion vectors for affinemotion compensation mode.

Following prediction, such as intra prediction or inter prediction of ablock, video encoder 200 may calculate residual data for the block. Theresidual data, such as a residual block, represents sample by sampledifferences between the block and a prediction block for the block,formed using the corresponding prediction mode. Video encoder 200 mayapply one or more transforms to the residual block, to producetransformed data in a transform domain instead of the sample domain. Forexample, video encoder 200 may apply a discrete cosine transform (DCT),an integer transform, a wavelet transform, or a conceptually similartransform to residual video data. Additionally, video encoder 200 mayapply a secondary transform following the first transform, such as amode-dependent non-separable secondary transform (MDNSST), a signaldependent transform, a Karhunen-Loeve transform (KLT), or the like.Video encoder 200 produces transform coefficients through application ofthe one or more transforms.

As noted above, following any transforms to produce transformcoefficients, video encoder 200 may perform quantization of thetransform coefficients. Quantization generally refers to a process inwhich transform coefficients are quantized to possibly reduce the amountof data used to represent the transform coefficients, providing furthercompression. By performing the quantization process, video encoder 200may reduce the bit depth associated with some or all of the transformcoefficients. For example, video encoder 200 may round an n-bit valuedown to an m-bit value during quantization, where n is greater than m.In some examples, to perform quantization, video encoder 200 may performa bitwise right-shift of the value to be quantized.

Following quantization, video encoder 200 may scan the transformcoefficients, producing a one-dimensional vector from thetwo-dimensional matrix including the quantized transform coefficients.The scan may be designed to place higher energy (and therefore lowerfrequency) transform coefficients at the front of the vector and toplace lower energy (and therefore higher frequency) transformcoefficients at the back of the vector. In some examples, video encoder200 may utilize a predefined scan order to scan the quantized transformcoefficients to produce a serialized vector, and then entropy encode thequantized transform coefficients of the vector. In other examples, videoencoder 200 may perform an adaptive scan. After scanning the quantizedtransform coefficients to form the one-dimensional vector, video encoder200 may entropy encode the one-dimensional vector, e.g., according tocontext-adaptive binary arithmetic coding (CABAC). Video encoder 200 mayalso entropy encode values for syntax elements describing metadataassociated with the encoded video data for use by video decoder 300 indecoding the video data. To perform CABAC, video encoder 200 may assigna context within a context model to a symbol to be transmitted.

As mentioned above, video encoder 200 and video decoder 300 may applyCABAC encoding and decoding to values of syntax elements. To apply CABACencoding to a syntax element, video encoder 200 may binarize the valueof the syntax element to form a series of one or more bits, which arereferred to as “bins.” In addition, video encoder 200 may identify acoding context, which may be referred to simply as a “context.” Thecoding context may identify probabilities of bins having particularvalues. For instance, a coding context may indicate a 0.7 probability ofcoding a 0-valued bin and a 0.3 probability of coding a 1-valued bin.After identifying the coding context, video encoder 200 may divide aninterval into a lower sub-interval and an upper sub-interval. One of thesub-intervals may be associated with the value 0 and the othersub-interval may be associated with the value 1. The widths of thesub-intervals may be proportional to the probabilities indicated for theassociated values by the identified coding context. If a bin of thesyntax element has the value associated with the lower sub-interval, theencoded value may be equal to the lower boundary of the lowersub-interval. If the same bin of the syntax element has the valueassociated with the upper sub-interval, the encoded value may be equalto the lower boundary of the upper sub-interval. To encode the next binof the syntax element, video encoder 200 may repeat these steps with theinterval being the sub-interval associated with the value of the encodedbit. When video encoder 200 repeats these steps for the next bin, videoencoder 200 may use modified probabilities based on the probabilitiesindicated by the identified coding context and the actual values of binsencoded.

When video decoder 300 performs CABAC decoding on a value of a syntaxelement, video decoder 300 may identify a coding context. Video decoder300 may then divide an interval into a lower sub-interval and an uppersub-interval. One of the sub-intervals may be associated with the value0 and the other sub-interval may be associated with the value 1. Thewidths of the sub-intervals may be proportional to the probabilitiesindicated for the associated values by the identified coding context. Ifthe encoded value is within the lower sub-interval, video decoder 300may decode a bin having the value associated with the lowersub-interval. If the encoded value is within the upper sub-interval,video decoder 300 may decode a bin having the value associated with theupper sub-interval. To decode a next bin of the syntax element, videodecoder 300 may repeat these steps with the interval being thesub-interval that contains the encoded value. When video decoder 300repeats these steps for the next bin, video decoder 300 may use modifiedprobabilities based on the probabilities indicated by the identifiedcoding context and the decoded bins. Video decoder 300 may thende-binarize the bins to recover the value of the syntax element.

In some instances, video encoder 200 may encode bins using bypass CABACcoding. It may be computationally less expensive to perform bypass CABACcoding on a bin than to perform regular CABAC coding on the bin.Furthermore, performing bypass CABAC coding may allow for a higherdegree of parallelization and throughput. Bins encoded using bypassCABAC coding may be referred to as “bypass bins.” Grouping bypass binstogether may increase the throughput of video encoder 200 and videodecoder 300. The bypass CABAC coding engine may be able to code severalbins in a single cycle, whereas the regular CABAC coding engine may beable to code only a single bin in a cycle. The bypass CABAC codingengine may be simpler because the bypass CABAC coding engine does notselect contexts and may assume a probability of ½ for both symbols (0and 1). Consequently, in bypass CABAC coding, the intervals are splitdirectly in half.

Video encoder 200 may further generate syntax data, such as block-basedsyntax data, picture-based syntax data, and sequence-based syntax data,e.g., in a picture header, a block header, a slice header, or othersyntax data, such as a sequence parameter set (SPS), picture parameterset (PPS), or video parameter set (VPS). Video decoder 300 may likewisedecode such syntax data to determine how to decode corresponding videodata.

In this manner, video encoder 200 may generate a bitstream includingencoded video data, e.g., syntax elements describing partitioning of apicture into blocks (e.g., CUs) and prediction and/or residualinformation for the blocks. Ultimately, video decoder 300 may receivethe bitstream and decode the encoded video data.

In general, video decoder 300 performs a reciprocal process to thatperformed by video encoder 200 to decode the encoded video data of thebitstream. For example, video decoder 300 may decode values for syntaxelements of the bitstream using CABAC in a manner substantially similarto, albeit reciprocal to, the CABAC encoding process of video encoder200. The syntax elements may define partitioning information forpartitioning a picture into CTUs, and partitioning of each CTU accordingto a corresponding partition structure, such as a QTBT structure, todefine CUs of the CTU. The syntax elements may further define predictionand residual information for blocks (e.g., CUs) of video data.

The residual information may be represented by, for example, quantizedtransform coefficients. Video decoder 300 may inverse quantize andinverse transform the quantized transform coefficients of a block toreproduce a residual block for the block. Video decoder 300 uses asignaled prediction mode (intra- or inter-prediction) and relatedprediction information (e.g., motion information for inter-prediction)to form a prediction block for the block. Video decoder 300 may thencombine the prediction block and the residual block (on asample-by-sample basis) to reproduce the original block. Video decoder300 may perform additional processing, such as performing a deblockingprocess to reduce visual artifacts along boundaries of the block.

Intra prediction involves a DC prediction mode, a planar predictionmode, and directional (or angular) prediction modes. Directionalprediction for square blocks uses directions between −135 degrees to 45degrees of the current block in the VVC test model 2 (VTM2) (J. Chen, Y.Ye, S. Kim, “Algorithm description for Versatile Video Coding and TestModel 2 (VTM2),” 11th JVET Meeting, Ljubljana, SI, July 2018,JVET-K1002), as illustrated in FIG. 2. FIG. 2 is a block diagramillustrating an example of intra prediction, with arrows pointing towardreference samples.

In VTM2, the block structure used for specifying the prediction blockfor intra prediction is not restricted to be square (width w=height h).Rectangular or non-square prediction blocks (w>h or w<h) can increasethe coding efficiency based on the characteristics of the content.

In such rectangular blocks, restricting the direction of intraprediction to be within −135 degrees to 45 degrees can result insituations where farther reference samples are used rather than closerreference samples for intra prediction. Such a design is likely to havean impact on the coding efficiency; it is more beneficial to have therange of restrictions relaxed so that closer reference samples (beyondthe −135 to 45-degree angle) can be used for prediction. An example ofsuch a case is given in FIG. 3. FIG. 3 is a conceptual diagram of anexample of 8×4 rectangular block where “closer” reference samples (upperright dashed circle 502) are not used, but farther reference samples(lower left dashed circle 504) may be used due to a restriction of anintra prediction direction to be in the range of −135 degrees to 45degrees. FIG. 4 is an illustration of wide angles that are adopted inVTM2.

During the 12^(th) JVET meeting, a modification of wide-angle intraprediction was adopted into VTM3 (See L. Zhao, X. Zhao, S. Liu, X. Li,“CE3-related: Unification of angular intra prediction for square andnon-square blocks,” 12^(th) JVET Meeting, Macau SAR, CN, Oct. 2018,JVET-L0279; J. Chen, Y. Ye, S. Kim, “Algorithm description for VersatileVideo Coding and Test Model 3 (VTM3),” 12^(th) JVET Meeting, Macau SAR,CN, Oct. 2018, JVET-L1002; B. Bross, J. Chen, S. Liu, “Versatile VideoCoding (Draft 3),” 12^(th) JVET Meeting, Macau SAR, CN, Oct. 2018,JVET-L1001). This adoption includes two modifications to unify theangular intra prediction for square and non-square blocks. Firstly,angular prediction directions are modified to cover diagonal directionsof all block shapes. Secondly, all angular directions are kept withinthe range between the bottom-left diagonal direction and the top-rightdiagonal direction for all block aspect ratios (square and non-square)as illustrated in FIGS. 5A-5C. FIGS. 5A, 5B, and 5C are illustrations ofmode mapping processes for intra prediction modes outside a diagonaldirection range. FIG. 5A illustrates a square block that does notrequire angular mode remapping. FIG. 5B illustrates angular moderemapping for a horizontal non-square block. FIG. 5C illustrates angularmode remapping for a vertical non-square block.

In addition, the number of reference samples in the top reference rowand left reference column are restricted to 2*width+1 and 2*height+1 forall block shapes. An illustration of wider angles that are adopted inVTM3 is provided in FIG. 6. FIG. 6 is a conceptual diagram illustratingwide angles (−1 to −14, and 67 to 80) in VVC Test Model 3 (VTM3) beyondmodes 2 and 66 for a total of 93 angular modes. Although VTM3 defines 95modes, for any block size only 67 modes are allowed. The exact modesthat are allowed depend on the ratio of block width to height. This isdone by restricting the mode range for certain blocks sizes.

Table 1, shown in FIG. 7, specifies the mapping table between an intraprediction mode (predModeIntra) and the angle parameter intraPredAnglein VTM3 (NET-L1001). The angular modes corresponding with non-squareblock diagonals are denoted with underlining. The vertical andhorizontal modes are denoted with italics. Square block diagonal modesare denoted with underlining and italics. The diagonal modes for a blockeach has an angle equal to an angle for a line between the lower-leftand top-right corners of the block or the top-left and bottom-rightcorners of the block. In this disclosure, angular modes with a positiveintraPredAngle value are referred to as positive angular modes (modeindex <18 or >50), while angular modes with a negative intraPredAnglevalue are referred to as negative angular modes (mode index >18 and<50).

The inverse angle parameter invAngle is derived based on intraPredAngleas follows:

$\begin{matrix}{{invAngle} = {{Round}\left( \frac{256*32}{intraPredAngle} \right)}} & \left( {2\text{-}1} \right)\end{matrix}$

Note that intraPredAngle values that are multiples of 32 (0, 32, 64,128, 256, 512) correspond with prediction from non-fractional referencearray samples, as is the case in the VTM3 specification.

Table 2, below, shows diagonal modes (i.e., diagonal intra predictionmodes) for blocks having various aspect ratios.

TABLE 2 Diagonal modes corresponding with various block aspect ratios.Block aspect ratio (width/height) Diagonal modes 1 (square) 2, 34, 66 28, 28, 72 4 12, 24, 76 8 14, 22, 78 16 16, 20, 80 1/2  −6, 40, 60 1/4 −10, 44, 56 1/8  −12, 46, 54 1/16 −14, 48, 52

The samples in the neighborhood of a coding block are used for intraprediction of the block. Typically, the reconstructed reference samplelines that are closest to the left and the top boundaries of the codingblock are used as the reference samples for intra prediction. However,VVC WD4 also enables other samples in the neighborhood of the codingblock to be used as reference samples. FIG. 8 illustrates the referencesample lines that may be used for intra prediction. In the example ofFIG. 8, reference sample lines are denoted using a multiple referenceline index (MRLIdx). For each coding block, an index is signaled thatindicates the reference line that is used.

The value of the signaled index may be different from the MRLIdxindicated by the signaled index. For instance, in VVC WD4, onlyreference lines with MRLIdx equal to 0, 1 and 3 can be used. In VVC WD4,the signaled index to the reference line used for coding the block(values 0, 1 and 2 indicating lines with MRLIdx 0, 1 and 3,respectively) is coded with a truncated unary codeword. Planar and DCmodes are not used when MRLIdx >0. In a more recent version of VVC,MRLIdx equal to 0, 1 and 2 can be used, and DC modes may be used whenMRLIdx >0.

To make the process of signaling intra prediction modes more efficient,video encoder 200 and video decoder 300 may identify one or more intraprediction modes as being “most probable modes” (MPMs) for a block. Ifthe intra prediction mode of the block is one of the MPMs for the block,an index to the MPM is signaled. If the intra prediction mode of theblock is not one of the MPMs for the block, an index to one of thenon-MPM intra prediction modes for the block may be signaled. Becausethere are typically far fewer MPMs for a block than non-MPM intraprediction modes, the index to the MPM may be signaled using fewer bitsthan the index to a non-MPM intra prediction mode. The following textfrom VVC WD4 in an example of a process for determining an intraprediction mode that determines MPMs for a block.

Input to this process are:

a luma location (xCb, yCb) specifying the top-left sample of the currentluma coding block relative to the top-left luma sample of the currentpicture,

a variable cbWidth specifying the width of the current coding block inluma samples,

a variable cbHeight specifying the height of the current coding block inluma samples.

In this process, the luma intra prediction mode IntraPredModeY[xCb][yCb]is derived.

Table 8-1 specifies the value for the intra prediction modeIntraPredModeY[xCb][yCb] and the associated names.

TABLE 8-1 Specification of intra prediction mode and associated namesIntra prediction mode Associated name 0 INTRA_PLANAR 1 INTRA_DC  2 . . .66 INTRA_ANGULAR2 . . . INTRA_ANGULAR66 81 . . . 83 INTRA_LT_CCLM,INTRA_ L_CCLM, INTRA_T_CCLM NOTE: The intra prediction modesINTRA_LT_CCLM, INTRA_L_CCLM and INTRA_T_CCLM are only applicable tochroma components.

IntraPredModeY[xCb][yCb] is derived by the following ordered steps:

The neighbouring locations (xNbA, yNbA) and (xNbB, yNbB) are set equalto (xCb−1, yCb+cbHeight−1) and (xCb+cbWidth−1, yCb−1), respectively.

For X being replaced by either A or B, the variables candIntraPredModeXare derived as follows:

The availability derivation process for a block as specified in clause6.4.X [Ed. (BB): Neighbouring blocks availability checking process tbd]is invoked with the location (xCurr, yCurr) set equal to (xCb, yCb) andthe neighbouring location (xNbY, yNbY) set equal to (xNbX, yNbX) asinputs, and the output is assigned to availableX.

The candidate intra prediction mode candIntraPredModeX is derived asfollows:

If one or more of the following conditions are true, candIntraPredModeXis set equal to INTRA_PLANAR.

The variable availableX is equal to FALSE.

CuPredMode[xNbX][yNbX] is not equal to MODE_INTRA andciip_flag[xNbX][yNbX] is not equal to 1.

pcm_flag[xNbX][yNbX] is equal to 1.

X is equal to B and yCb−1 is less than((yCb>>CtbLog2SizeY)<<CtbLog2SizeY).

Otherwise, candIntraPredModeX is set equal toIntraPredModeY[xNbX][yNbX].

The variables ispDefaultMode1 and ispDefaultMode2 are defined asfollows:

If IntraSubPartitionsSplitType is equal to ISP_HOR_SPLIT,ispDefaultMode1 is set equal to INTRA_ANGULAR18 and ispDefaultMode2 isset equal to INTRA_ANGULAR5.

Otherwise, ispDefaultMode1 is set equal to INTRA_ANGULAR50 andispDefaultMode2 is set equal to INTRA_ANGULAR63.

The candModeList[x] with x=0 . . . 5 is derived as follows:

If candIntraPredModeB is equal to candIntraPredModeA andcandIntraPredModeA is greater than INTRA_DC, candModeList[x] with x=0 .. . 5 is derived as follows:

If IntraLumaRefLineIdx[xCb][yCb] is equal to 0 andIntraSubPartitionsSplitType is equal to ISP_NO_SPLIT, the followingapplies:candModeList[0]=candIntraPredModeA  (8-8)candModeList[1]=INTRA_PLANAR  (8-9)candModeList[2]=INTRA_DC  (8-10)candModeList[3]=2+((candIntraPredModeA+61)% 64)  (8-11)candModeList[4]=2+((candIntraPredModeA−1)% 64)  (8-12)candModeList[5]=2+((candIntraPredModeA+60)% 64)  (8-13)

Otherwise (IntraLumaRefLineIdx[xCb][yCb] is not equal to 0 orIntraSubPartitionsSplitType is not equal to ISP_NO_SPLIT), the followingapplies:candModeList[0]=candIntraPredModeA  (8-14)candModeList[1]=2+((candIntraPredModeA+61)% 64)  (8-15)candModeList[2]=2+((candIntraPredModeA−1)% 64)  (8-16)

If one of the following conditions is true,

IntraSubPartitionsSplitType is equal to ISP_HOR_SPLIT andcandIntraPredModeA is less than INTRA_ANGULAR34,

IntraSubPartitionsSplitType is equal to ISP VER SPLIT andcandIntraPredModeA is greater than or equal to INTRA_ANGULAR34,

IntraLumaRefLineIdx[xCb][yCb] is not equal to 0,

the following applies:candModeList[3]=2+((candIntraPredModeA+60)% 64)  (8-17)candModeList[4]=2+(candIntraPredModeA % 64)  (8-18)candModeList[5]=2+((candIntraPredModeA+59)% 64)  (8-19)

Otherwise, the following applies:candModeList[3]=ispDefaultMode1  (8-20)candModeList[4]=ispDefaultMode2  (8-21)candModeList[5]=INTRA_PLANAR  (8-22)

Otherwise if candIntraPredModeB is not equal to candIntraPredModeA andcandIntraPredModeA or candIntraPredModeB is greater than INTRA_DC, thefollowing applies:

The variables minAB and maxAB are derived as follows:minAB=Min(candIntraPredModeA,candIntraPredModeB)  (8-23)maxAB=Max(candIntraPredModeA,candIntraPredModeB)  (8-24)

If candIntraPredModeA and candIntraPredModeB are both greater thanINTRA_DC, candModeList[x] with x=0 . . . 5 is derived as follows:candModeList[0]=candIntraPredModeA  (8-25)candModeList[1]=candIntraPredModeB  (8-26)

If IntraLumaRefLineIdx[xCb][yCb] is equal to 0 andIntraSubPartitionsSplitType is equal to ISP_NO_SPLIT, the followingapplies:candModeList[2]=INTRA_PLANAR  (8-27)candModeList[3]=INTRA_DC  (8-28)

If maxAB-minAB is in the range of 2 to 62, inclusive, the followingapplies:candModeList[4]=2+((maxAB+61)% 64)  (8-29)candModeList[5]=2+((maxAB−1)% 64)  (8-30)

Otherwise, the following applies:candModeList[4]=2+((maxAB+60)%64)  (8-31)candModeList[5]=2+((maxAB)%64)  (8-32)

Otherwise (IntraLumaRefLineIdx[xCb][yCb] is not equal to 0 orIntraSubPartitionsSplitType is not equal to ISP_NO_SPLIT), the followingapplies:

When IntraSubPartitionsSplitType is not equal to ISP_NO_SPLIT, andabs(candIntraPredModeB−ispDefaultMode1) is less thanabs(candIntraPredModeA−ispDefaultMode1), the following applies:candModeList[0]=candIntraPredModeB  (8-33)candModeList[1]=candIntraPredModeA  (8-34)

If maxAB-minAB is equal to 1, the following applies:candModeList[2]=2+((minAB+61)% 64)  (8-35)candModeList[3]=2+((maxAB−1)% 64)  (8-36)candModeList[4]=2+((minAB+60)% 64)  (8-37)candModeList[5]=2+(maxAB % 64)  (8-38)

Otherwise if maxAB-minAB is equal to 2, the following applies:candModeList[2]=2+((minAB−1)% 64)  (8-39)candModeList[3]=2+((minAB+61)% 64)  (8-40)candModeList[4]=2+((maxAB−1)% 64)  (8-41)candModeList[5]=2+((minAB+60)% 64)  (8-42)

Otherwise if maxAB-minAB is greater than 61, the following applies:candModeList[2]=2+((minAB−1)% 64)  (8-43)candModeList[3]=2+((maxAB+61)% 64)  (8-44)candModeList[4]=2+(minAB % 64)  (8-45)candModeList[5]=2+((maxAB+60)% 64)  (8-46)

Otherwise, the following applies:candModeList[2]=2+((minAB+61)% 64)  (8-47)candModeList[3]=2+((minAB−1)% 64)  (8-48)candModeList[4]=2+((maxAB+61)% 64)  (8-49)candModeList[5]=2+((maxAB−1)% 64)  (8-50)

Otherwise (candIntraPredModeA or candIntraPredModeB is greater thanINTRA_DC), candModeList[x] with x=0 . . . 5 is derived as follows:

If IntraLumaRefLineIdx[xCb][yCb] is equal to 0 andIntraSubPartitionsSplitType is equal to ISP_NO_SPLIT, the followingapplies:candModeList[0]=candIntraPredModeA  (8-51)candModeList[1]=candIntraPredModeB  (8-52)candModeList[2]=1−minAB  (8-53)candModeList[3]=2+((maxAB+61)% 64)  (8-54)candModeList[4]=2+((maxAB−1)% 64)  (8-55)candModeList[5]=2+((maxAB+60)% 64)  (8-56)

Otherwise, if IntraLumaRefLineIdx[xCb][yCb] is not equal to 0, thefollowing applies:candModeList[0]=maxAB  (8-57)candModeList[1]=2+((maxAB+61)% 64)  (8-58)candModeList[2]=2+((maxAB−1)% 64)  (8-59)candModeList[3]=2+((maxAB+60)% 64)  (8-60)candModeList[4]=2+(maxAB % 64)  (8-61)candModeList[5]=2+((maxAB+59)% 64)  (8-62)

Otherwise (IntraSubPartitionsSplitType is not equal to ISP_NO_SPLIT),the following applies:candModeList[0]=INTRA_PLANAR  (8-63)candModeList[1]=maxAB  (8-64)candModeList[2]=2+((maxAB+61)% 64)  (8-65)candModeList[3]=2+((maxAB−1)% 64)  (8-66)candModeList[4]=2+((maxAB+60)% 64)  (8-67)candModeList[5]=2+(maxAB % 64)  (8-68)

Otherwise, the following applies:

If IntraLumaRefLineIdx[xCb][yCb] is equal to 0 andIntraSubPartitionsSplitType is equal to ISP_NO_SPLIT, the followingapplies:candModeList[0]=candIntraPredModeA  (8-69)candModeList[1]=(candModeList[0]==INTRA_PLANAR)?INTRA_DC:  (8-70)INTRA_PLANAR candModeList[2]=INTRA_ANGULAR50  (8-71)candModeList[3]=INTRA_ANGULAR18  (8-72)candModeList[4]=INTRA_ANGULAR46  (8-73)candModeList[5]=INTRA_ANGULAR54  (8-74)

Otherwise, if IntraLumaRefLineIdx[xCb][yCb] is not equal to 0, thefollowing applies:candModeList[0]=INTRA_ANGULAR50  (8-75)candModeList[1]=INTRA_ANGULAR18  (8-76)candModeList[2]=INTRA_ANGULAR2  (8-77)candModeList[3]=INTRA_ANGULAR34  (8-78)candModeList[4]=INTRA_ANGULAR66  (8-79)candModeList[5]=INTRA_ANGULAR26  (8-80)

Otherwise, if IntraSubPartitionsSplitType is equal to ISP_HOR_SPLIT, thefollowing applies:candModeList[0]=INTRA_PLANAR  (8-81)candModeList[1]=INTRA_ANGULAR18  (8-82)candModeList[2]=INTRA_ANGULAR25  (8-83)candModeList[3]=INTRA_ANGULAR10  (8-84)candModeList[4]=INTRA_ANGULAR65  (8-85)candModeList[5]=INTRA_ANGULAR50  (8-86)

Otherwise, if IntraSubPartitionsSplitType is equal to ISP VER SPLIT, thefollowing applies:candModeList[0]=INTRA_PLANAR  (8-87)candModeList[1]=INTRA_ANGULAR50  (8-88)candModeList[2]=INTRA_ANGULAR43  (8-89)candModeList[3]=INTRA_ANGULAR60  (8-90)candModeList[4]=INTRA_ANGULAR3  (8-91)candModeList[5]=INTRA_ANGULAR18(8-92)

IntraPredModeY[xCb][yCb] is derived by applying the following procedure:

If intra_luma_mpm_flag[xCb][yCb] is equal to 1, theIntraPredModeY[xCb][yCb] is set equal tocandModeList[intra_luma_mpm_idx[xCb][yCb]].

Otherwise, IntraPredModeY[xCb][yCb] is derived by applying the followingordered steps:

When candModeList[i] is greater than candModeList[j] for i=0 . . . 4 andfor each i, j=(i+1) . . . 5, both values are swapped as follows:(candModeList[i],candModeList[j])=Swap(candModeList[i],candModeList[j])  (8-93)

IntraPredModeY[xCb][yCb] is derived by the following ordered steps:

IntraPredModeY[xCb][yCb] is set equal tointra_luma_mpm_remainder[xCb][yCb].

For i equal to 0 to 5, inclusive, when IntraPredModeY[xCb][yCb] isgreater than or equal to candModeList[i], the value ofIntraPredModeY[xCb][yCb] is incremented by one.

The variable IntraPredModeY[x][y] with x=xCb . . . xCb+cbWidth−1 andy=yCb . . . yCb+cbHeight−1 is set to be equal toIntraPredModeY[xCb][yCb].

Intra sub-partition coding (ISP) (see S. De Luxán Hernández, V. George,J. Ma, T. Nguyen, H. Schwarz, D. Marpe, T. Wiegand (HHI), “CE3: IntraSub-Partitions Coding Mode,” JVET-M0102) is a method by which a codingblock is split into two or four subblocks. Each subblock within a blockis reconstructed in decoding order before the reconstruction of thesubsequent subblock in decoding order. In VVC WD4, ISP is only appliedto luma coding blocks. The reference samples for ISP-coded blocks arerestricted to be from the reference line that is closest to the codingblock (e.g., MRLIdx=0 as shown in FIG. 8). Examples of splitting areshown in FIG. 9 and FIG. 10.

One bit is used to signal whether a coding block is split into ISPs anda second bit is used to indicate the split type: horizontal or vertical.Based on the intra mode and the split type used, two different classesof processing orders may be used, which are referred to as normal andreversed order. In the normal order, the first sub-partition to beprocessed is the one containing the top-left sample of the CU and thencontinuing downwards (horizontal split) or rightwards (vertical split).On the other hand, the reverse processing order either starts with thesub-partition containing the bottom-left sample of the CU (horizontalsplit) and continues upwards or starts with sub-partition containing thetop-right sample of the CU and continues leftwards (vertical split).

A variation of ISP that uses only the normal processing order is used inJVET WD4. It is to be noted that the terms subblock and sub-partitionsare used interchangeably in this document, and both refer to the blocksobtained by partitioning a coding block using ISP.

Some syntax and semantics associated with ISP in JVET WD4 are shownbelow, with relevant syntax is enclosed in tags <!> . . . </!>

Syntax table of coding unit coding_unit( x0, y0, cbWidth, cbHeight,treeType ) { Descriptor . . .  } else {   if( treeType = = SINGLE_TREE || treeType = = DUAL_TREE_LUMA ) {    if( ( y0 % CtbSizeY ) > 0 )    intra_luma_ref_idx[ x0 ][ y0 ] ae(v) <!>  if (intra_luma_ref_idx[ x0][ y0 ] = = 0 &&     ( cbWidth <= MaxTbSizeY | | cbHeight <=    MaxTbSizeY ) &&     ( cbWidth * cbHeight > MinTbSizeY * MinTbSizeY))     intra_subpartitions_mode_flag[ x0 ][ y0 ] ae(v)    if(intra_subpartitions_mode_flag[ x0 ][ y0 ] = = 1 &&     cbWidth <=MaxTbSizeY && cbHeight <=     MaxTbSizeY )    intra_subpartitions_split_flag[ x0 ][ y0 ] ae(v)</!>    if(intra_luma_ref_idx[ x0 ][ y0 ] = = 0 &&    intra_subpartitions_mode_flag[ x0 ][ y0 ] = = 0 )    intra_luma_mpm_flag[ x0 ][ y0 ] ae(v)    if( intra_luma_mpm_flag[ x0][ y0 ] )     intra_luma_mpm_idx[ x0 ][ y0 ] ae(v) . . .

Syntax table of transform tree transform_tree( x0, y0, tbWidth,tbHeight, treeType) { Descriptor <!> InferTuCbfLuma = 1  if(IntraSubPartSplitType = = NO_ISP_SPLIT ) {</!>   if( tbWidth >MaxTbSizeY | | tbHeight > MaxTbSizeY ) {     trafoWidth = ( tbWidth >MaxTbSizeY ) ? (tbWidth / 2) :     tbWidth     trafoHeight = (tbHeight > MaxTbSizeY ) ? (tbHeight / 2) :     tbHeight    transform_tree( x0, y0, trafoWidth, trafoHeight )     if( tbWidth >MaxTbSizeY )  transform_tree( x0 + trafoWidth, y0, trafoWidth,trafoHeight,  treeType )     if( tbHeight > MaxTbSizeY ) transform_tree( x0, y0 + trafoHeight, trafoWidth, trafoHeight, treeType )     if( tbWidth > MaxTbSizeY && tbHeight > MaxTbSizeY ) transform_tree( x0 + trafoWidth, y0 + trafoHeight,  trafoWidth,trafoHeight, treeType )   } else {     transform_unit( x0, y0, tbWidth,tbHeight, treeType, 0 )   } <!> }else if( IntraSubPartitionsSplitType == ISP_HOR_ SPLIT ) {   trafoHeight = tbHeight / NumIntraSubPartitions  for( partIdx = 0; partIdx < NumIntraSubPartitions; partIdx++)    transform_unit( x0, y0 + trafoHeight * partIdx, tbWidth,    trafoHeight, treeType, partIdx )  } else if(IntraSubPartitionsSplitType = = ISP_VER_SPLIT ){    trafoWidth = tbWidth/ NumIntraSubPartitions    for( partIdx = 0; partIdx <NumIntraSubPartitions; partIdx++)     transform_unit( x0 + trafoWidth *partIdx, y0, trafoWidth,     tbHeight, treeType, partIdx )    }</!> }Semantics of Coding Unit<!>intra_subpartitions_mode_flag[x0][y0] equal to 1 specifies that thecurrent intra coding unit is partitioned intoNumIntraSubPartitions[x0][y0] rectangular transform block subpartitions.intra_subpartitions_mode_flag[x0][y0] equal to 0 specifies that thecurrent intra coding unit is not partitioned into rectangular transformblock subpartitions. When intra_subpartitions_mode_flag[x0][y0] is notpresent, it is inferred to be equal to 0.intra_subpartitions_split_flag[x0][y0] specifies whether the intrasubpartitions split type is horizontal or vertical. Whenintra_subpartitions_mode_flag[x0][y0] is not present, it is inferred tobe equal to 0. The variable IntraSubPartitionsSplitType specifies thetype of split used for the current luma coding block as illustrated inTable 2-3. IntraSubPartitionsSplitType is derived as follows:

-   -   If intra_subpartitions_mode_flag[x0][y0] is equal to 0,        IntraSubPartitionsSplitType is set equal to 0.    -   Otherwise, the IntraSubPartitionsSplitType is set equal to        1+intra_subpartitions_split_flag[x0][y0].

TABLE 2-3 Name association to IntraSubPartitionsSplitTypeIntraSubPartitions Name of IntraSubPartitions SplitType SplitType 0ISP_NO_SPLIT 1 ISP_HOR_SPLIT 2 ISP_VER_SPLITThe variable NumIntraSubPartitions specifies the number of transformblock subpartitions an intra luma coding block is divided into.NumIntraSubPartitions is derived as follows:

-   -   If IntraSubPartitionsSplitType is equal to ISP_NO_SPLIT,        NumIntraSubPartitions is set equal to 1.    -   Otherwise, if one of the following conditions is true,        NumIntraSubPartitions is set equal to 2:        -   cbWidth is equal to 4 and cbHeight is equal to 8,        -   cbWidth is equal to 8 and cbHeight is equal to 4.    -   Otherwise, NumIntraSubPartitions is set equal to 4.</!>

Affine linear weighted intra prediction (ALWIP) (e.g., as described inJ. Pfaff et al., “Affine linear weighted intra prediction (CE3-4.1,CE3-4.2)”, Joint Video Experts Team (WET) of ITU-T SG 16 WP 3 andISO/IEC JTC 1/SC 29/WG 11, 14th Meeting: Geneva, CH, 19-27 Mar. 2019,document JVET-N0217 (hereinafter “WET-N0217”)) generates a prediction ofa block (i.e., a prediction block) from the neighboring referencesamples using an affine linear weighted prediction model. Theneighboring samples are first processed (e.g., in some cases,neighboring samples are down-sampled) and the processed (e.g.,down-sampled) samples are then used to derive (using an affine model) aset of reduced samples which resembles an intermediate down-sampledversion of the predicted samples. A final prediction is obtained byup-sampling (as necessary) the intermediate values. Note that ALWIP mayalso be referred to as matrix intra prediction (MIP).

An illustration of the ALWIP process is given in FIG. 11. The ALWIPprocess of FIG. 11 may be performed by video encoder 200 and videodecoder 300. The reference samples of the block (also referred to asboundary samples) are down-sampled to obtain reduced boundary samples.The vector representation of the boundary samples, bdry_(red), ismultiplied with a matrix A_(k) and an offset/bias term b_(k) is added toobtain a down-sampled version of the predicted block, pred_(red). Thefinal prediction is obtained by up-sampling these predicted samplespred_(red) along with the boundary samples. The matrix A_(k) and anoffset/bias vector b_(k) are chosen based on a mode value indicated forthe block. A combination of a matrix A_(k) and an offset/bias vectorb_(k) may be referred to herein as an “ALWIP mode.”

The derivation of intermediate predicted samples uses an affine linearweighted prediction model. Three types (i.e., ALWIP types) are defined,and the number of the intermediate samples derived differ for each typeas follows:

-   -   1) 4×4 for block sizes of width and height both equal to 4. In        other words, there are 16 intermediate samples for blocks having        sizes of 4×4.    -   2) 8×8 for block sizes of width and height both less than equal        to 8 except when both width and height are equal to 4 (i.e.,        4×8, 8×4 and 8×8 blocks). In other words, there are 64        intermediate samples for blocks having sizes of H×W, where 4<H≤8        and 4<W≤8, or H=4 and 4<W<8, or W=4 and 4<H<8    -   3) 16×16 for blocks where at least one of width and height is        greater than 8. In other words, there are 256 intermediate        samples for blocks having sizes of H×W, there either H>8 or W>8.        In each of these three cases, different numbers of ALWIP modes        are used: 35, 19, and 11, respectively. In other words, for        ALWIP type 1, there are 35 different available ALWIP modes; for        ALWIP type 2, there are 19 different available ALWIP modes; and        for ALWIP type 3, there are 11 different ALWIP modes available.        Each of the different ALWIP modes may correspond to a different        combination of a matrix A_(k) and an offset/bias value b_(k).

The signaling of the ALWIP includes:

-   -   a) A flag (alwip_flag) to indicate that the current block is        coded with ALWIP.    -   b) When the current block is coded with ALWIP, another flag is        signaled to indicate whether the current block is coded with an        ALWIP-most probable mode (MPM) mode or not.        -   a. If the block is coded with an ALWIP-MPM mode, an MPM            index is signaled. Derivation of the ALWIP-MPM mode is            described in this disclosure below.        -   b. Else, an index to a remaining mode value is signaled. The            remaining mode value indicates an ALWIP mode other than the            ALWIP-MPM mode.

The alwip_flag is context coded with four contexts allowed:

-   -   If block width >2*height or height >2*width, context 3 is used.    -   Else, context ctxId is used, where ctxId is derived as follows:        -   Initialize ctxId to 0.        -   If the left neighboring block is coded with ALWIP, ctxId++            (i.e., increment ctxId).        -   If the above neighboring block is coded with ALWIP, ctxId++.

The derivation of the ALWIP MPM modes involves the following steps:

-   -   1) LeftIntraMode and AboveIntraMode are initialized to −1.    -   2) If the left neighboring block is intra coded:        -   a. If the left neighboring block is coded with ALWIP mode L            (i.e., if the left neighboring block is coded with ALWIP,            let the ALWIP mode of the left neighboring block be denoted            as L):            -   i. If L is of the same ALWIP type as the current block,                then LeftIntraMode is set equal to L.        -   b. Otherwise, if the left neighboring block is not coded            with an ALWIP mode, the intra mode of the left neighboring            block is mapped to an ALWIP mode of the same type as the            current block and assigned to LeftIntraMode.    -   3) If the above neighboring block is intra coded:        -   a. If the above neighboring block is coded with ALWIP mode A            (i.e., if the above neighboring block is coded with ALWIP,            let the ALWIP mode of the above neighboring block be denoted            as A):            -   i. If A is of the same ALWIP type as the current block,                then AboveIntraMode is set equal to A.        -   b. Otherwise, if the above neighboring block is not coded            with an ALWIP mode, the intra mode of the above neighboring            block is mapped to an ALWIP mode of the same type as the            current block and assigned to AboveIntraMode.    -   4) The MPMs are then derived based on LeftIntraMode and        AboveIntraMode. In other words, a first ALWIP-MPM is set equal        to LeftIntraMode and a second ALWIP-MPM is set equal to        AboveIntraMode. If LeftIntraMode remains equal to −1 or        AboveIntraMode remains equal to −1, the corresponding MPMs are        unavailable.        In the rest of the document, blocks coded with ALWIP may be        referred to as ALWIP-coded blocks or ALWIP blocks; other blocks        (e.g., blocks coded with regular intra prediction, intra        sub-partitions, or multiple reference lines) may be referred to        as non-ALWIP blocks.

There are several problems in the design of ALWIP (i.e., MIP). Forexample, the context derivation of the flag indicating whether a currentblock is coded using ALWIP mode (e.g., alwip_flag) uses the alwip_flagvalues from left and above neighboring blocks. The value of analwip_flag of the above neighboring block is used even when the aboveneighboring block belongs to a different CTU row. This createsadditional storage requirements. For instance, if r refers to the CTUboundary between the current CTU row and the previous CTU row, thealwip_flag of all the blocks from the previous CTU row that shares aboundary r need to be stored. In a worst-case scenario of 4×4 blocks ina 4K picture, the number of bytes required would be 3840/4 (number ofblocks)×1 (bits per flag value)=120 bytes. Providing storage for thealwip_flag values of all the blocks from the previous CTU row increasesmemory storage requirements of video encoder 200 and video decoder 300,thereby potentially increasing the cost and complexity of video encoder200 and video decoder 300.

In another example of a problem with the design of ALWIP, there are 35matrices/modes specified for 4×4 blocks. These 35 matrices/modesrepresent nearly 25% of the parameters needed for ALWIP. The compressionefficiency when enabling ALWIP 4×4 blocks is nearly 0.05% and storagerequired around 2 KB (to store the 35 matrices and offset/bias vectors).Thus, the storage burden on encoder/decoder implementations is undue forthe efficiency obtained. FIG. 12 is a table illustrating the number ofmatrix parameters and offset parameters for each ALWIP type in VVC WD4.

During the most-probable mode (MPM) derivation of non-ALWIP blocks, theintra mode used for the left and above neighboring blocks are checkedand used when available. For instance, when deriving the ALWIP MPMmodes, a video coder (e.g., video encoder 200 and video decoder 300)determines whether the left neighboring block is available and, if so,the video coder determines whether the left neighboring block is intracoded and, if so, the video coder determines whether or not the leftneighboring block is coded using an ALWIP mode. Similarly, the videocoder also determines whether the above neighboring block is availableand, if so, the video coder determines whether the above neighboringblock is intra coded and, if so, the video coder determines whether ornot the above neighboring block is coded using an ALWIP mode. Fornon-ALWIP blocks (i.e., blocks not coded using an ALWIP mode), modevalues correspond to angular intra prediction modes or Planar/DC intraprediction modes. Except in trivial cases, one set of matrixcoefficients (e.g., a set of matrix coefficients for an ALWIP mode) usedin ALWIP may not correspond to any of the intra modes used in non-ALWIPblocks. ALWIP currently uses a first mapping table to approximate themapping of the ALWIP matrix to one of the intra modes. This approximatedvalue is then considered as the intra mode of the neighboring block tobe used in the MPM derivation of the non-ALWIP block. In other words,when a left neighboring block is coded using a non-ALWIP intraprediction mode, a video coder (e.g., video encoder 200 or video decoder300) sets a first ALWIP-MPM to the approximated value for the leftneighboring block. Similarly, when an above neighboring block is codedusing a non-ALWIP intra prediction mode, the video coder sets a secondALWIP-MPM to the approximated value for the above neighboring block.This may result in inefficient compression, e.g., because of error inthe approximation. Moreover, the mapping table requires additionalstorage and adds lookup operations in the MPM derivation process. Theadditional storage adds to the cost and complexity of video encoder 200and video decoder 300. The additional lookup operations may slow downthe encoding and decoding processes.

This problem may also apply to the chroma Direct Mode (DM) mode, wherethe intra mode used for the chroma block is copied from a collocatedintra block. When the collocated intra block is ALWIP coded, the firstmapping table is used to derive the chroma DM mode from the ALWIP blockmatrix/mode. In other words, a luma block collocated with a chroma blockmay be coded using an ALWIP mode but the chroma block cannot be codedusing any ALWIP mode. Thus, if the chroma block is to be coded using thechroma DM mode in which the intra prediction mode of the luma block isinherited by the chroma block, it may be necessary for a video coder(e.g., video encoder 200 or video decoder 300) to convert from the ALWIPmode of the luma block to a non-ALWIP intra prediction mode for use inthe chroma block. This conversion is an approximation that may reducecoding efficiency. Furthermore, this conversion may require additionalstorage for a mapping table and may add lookup operations, which mayincrease the cost and complexity of the video coder and may slow theencoding and decoding processes.

Similar to the examples in the previous paragraphs, during the MPMderivation of an ALWIP block, intra modes from the left and aboveneighboring blocks are checked and used when available. When theneighboring block is a non-ALWIP block, the intra mode of the non-ALWIPblock may not correspond to the matrices/modes used by the ALWIP block.In other words, different ALWIP modes available for use with a currentblock depending on the size of the current block and the intra mode ofan above or left neighboring block of the current block may notcorrespond to any of the ALWIP modes available for use with the currentblock. Hence, a second mapping table is used to map the intra mode ofthe non-ALWIP block to the matrix/mode of the ALWIP block. This mayresult in inefficiency in compression. Moreover, the second mappingtable requires additional storage and adds lookup operations in the MPMderivation process. If a neighboring block is coded with combinedintra/inter mode (CIIP), the neighboring block is considered (e.g., byvideo encoder 200 and video decoder 300) as a non-intra-coded mode andis marked as unavailable. If a neighboring block is coded with intrablock copy mode (IBC), the block is considered as a non-intra-coded modeand is marked as unavailable.

This disclosure describes techniques that may improve the design ofALWIP mode. The techniques of this disclosure may reduce the cost andcomplexity of video coders, such as video encoder 200 and video decoder300, and may increase the speed of encoding and decoding processes. Thetechniques and examples of this disclosure may be used by video encoder200 and video decoder 300 individually or in any combination.

In accordance with a first technique of this disclosure, when an aboveneighboring block belongs to a different CTU than a current block (i.e.,a block that a video coder (e.g., video encoder 200 or video decoder300) is currently coding), the above neighboring block is considered tobe unavailable for the purpose of derivation of the context for analwip_flag. For example, a derivation process of the context foralwip_flag may be modified as follows, with <!> . . . </!>tagsindicating additions:

The alwip_flag is context coded with four contexts allowed:

-   -   If block width >2*height or height >2*width, context 3 is used.    -   Else, context ctxId is used, where ctxId is derived as follows:        -   Initialize ctxId to 0        -   If the left neighboring block is coded with ALWIP, ctxId++.        -   If the above neighboring block is coded with ALWIP <!>and            the above neighboring block is in the same CTU as the            current block</!>, ctxId++            Thus, in this example, video encoder 200 and video decoder            300 may avoid the need to store data indicating whether            blocks in a CTU row above a CTU row containing the current            block are coded using an ALWIP mode. Avoiding the need to            store such data may reduce the cost and complexity of video            encoder 200 and video decoder 300.

In some examples, the value of an alwip_flag from an above CTU row maybe inferred to be equal to a particular value (e.g., 0) for purposesderiving the context of alwip_flag for the current block. In otherwords, video encoder 200 and video decoder 300 may assume that thealwip_flag values for above neighboring blocks that are in an above CTUrow all have the same particular value. In this way, video encoder 200and video decoder 300 may avoid the need to store data indicatingwhether the blocks in the CTU row above the CTU row containing thecurrent block are coded using an ALWIP mode, with the resultingpotential reductions of cost and complexity for video encoder 200 andvideo decoder 300.

Thus, in accordance with an example of the first technique of thisdisclosure, a video coder (e.g., video encoder 200 or video decoder 300)may determine a context for an ALWIP syntax element (e.g., alwip_flag).In this example, the ALWIP syntax element indicates whether a currentblock is coded with ALWIP. Furthermore, in this example, an aboveneighbor block is determined to be unavailable for determining thecontext based on the above neighbor block being in a different CTU fromthe current block, the above neighbor block being an above neighbor ofthe current block. In this example, the video coder may code the ALWIPsyntax element based on the context. For instance, the video coder mayuse the context in CABAC coding of the ALWIP syntax element.

In accordance with a second technique of this disclosure, a constraintis introduced to disable ALWIP for blocks less than a particularthreshold of width, w_(T), and height, h_(T). In other words, a videocoding standard (e.g., VVC, etc.) may impose a constraint that disablesALWIP for blocks that have a width less than a threshold width or aheight less than a threshold height. Thus, a video coding standard mayspecify that blocks having widths less than w_(T) and heights less thanh_(T) cannot be coded using ALWIP. For example, the constraint mayprovide that ALWIP is disabled for blocks with widths less than 8 andheights less than 8. In some examples, ALWIP-related syntax elements areconditioned based on such block size restrictions. As noted above, e.g.,with respect to FIG. 12, the coding of small blocks with ALWIP mayresult in high storage requirements but relatively modest gains incoding efficiency. Introducing this constraint may reduce the number ofparameters that video encoder 200 and video decoder 300 may need tostore to implement ALWIP, thereby potentially reducing complexity andcost of video encoder 200 and video decoder 300. Thus, in accordancewith the second technique of this disclosure, a constraint may beimposed that disables ALWIP for blocks that have widths less than athreshold width (e.g., 8) or heights less than a threshold height (e.g.,8).

In accordance with a third technique of this disclosure, when anALWIP-coded neighboring block is considered/tested in the MPM derivationof a non-ALWIP coded block, the neighboring block may be consideredunavailable (or inter-coded) and/or the value of the intra mode of sucha neighboring block may be inferred to be a particular value (e.g.,planar mode, DC mode, or another intra prediction mode) for the MPMderivation of the non-ALWIP coded block. For ease of explanation, thisdisclosure may refer to the particular value as a default value. In thisway, video encoder 200 and video decoder 300 may avoid the need to storea mapping table to map ALWIP modes to non-ALWIP-intra prediction modesand may avoid lookup operations into the mapping table. This may reducethe storage requirements of video encoder 200 and video decoder 300,which may reduce the cost and complexity of video encoder 200 and videodecoder 300.

Thus, in accordance with the third technique of this disclosure, a videocoder (e.g., video encoder 200 or video decoder 300) may perform an MPMderivation process that derives one or more MPMs for a current blockthat is not coded using ALWIP. As part of performing the MPM derivationprocess, the video coder may determine whether a neighboring block ofthe current block is an ALWIP-coded neighboring block. Based on theneighboring block being an ALWIP-coded neighboring block, the videocoder may determine that a value of an intra prediction mode of theneighboring block is a default value. The video coder may then includean intra prediction mode corresponding to the default value as one ofthe one or more MPMs. If the neighboring block is not ALWIP-coded, thevideo coder may determine that the one or more MPMs include the intraprediction mode of the neighboring block. The video coder may code(e.g., encode or decode) the current block based on one of the MPMs forthe current block or based on another intra prediction mode.

Furthermore, in some examples, when a chroma block is coded with the DMmode (i.e., the intra prediction mode of the chroma block is inheritedfrom a collocated luma block) and the collocated luma block (or moreparticularly, a luma block used to derive the DM mode of the chromablock) is coded with ALWIP, the intra mode of the collocated block maybe determined, e.g., inferred, to be a default value (e.g., Planar). Inthis way, video encoder 200 and video decoder 300 may avoid the need tostore a mapping table to map ALWIP modes to non-ALWIP-intra predictionmodes and may avoid lookup operations into the mapping table. This mayreduce the storage requirements of video encoder 200 and video decoder300, which may reduce the cost and complexity of video encoder 200 andvideo decoder 300.

Thus, in some examples where a chroma block is coded with a DM mode, avideo coder (e.g., video encoder 200 or video decoder 300) may determinewhether a collocated luma block is coded with ALWIP, where thecollocated luma block is collocated with the chroma block. Based on thecollocated luma block being coded with ALWIP, the video coder maydetermine, e.g., infer, that an intra prediction mode of the collocatedluma block is a default value (e.g., planar mode), such as the planarmode or another intra prediction mode. The video coder may code (e.g.,encode or decode) the chroma block using an intra prediction modecorresponding to the default value. For instance, to encode the chromablock using the intra prediction mode corresponding to the defaultvalue, video encoder 200 may generate a prediction block using the intraprediction mode. Video encoder 200 may then generate residual data forthe chroma block based on samples of the chroma block and the predictionblock. To decode the chroma block using the intra prediction modecorresponding to the default value, video decoder 300 may generate aprediction block using the intra prediction mode. Video decoder 300 maythen reconstruct the chroma block based on the prediction block andresidual data for the chroma block.

In accordance with a fourth technique of this disclosure, when anon-ALWIP neighboring block is used in the MPM derivation of an ALWIPblock, the neighboring block may be considered unavailable (orinter-coded) and/or the neighboring mode value may be assigned to adefault value for the MPM derivation of the ALWIP block. In other words,when determining ALWIP-MPMs for an ALWIP-coded block and a neighboringblock is not coded using ALWIP, video encoder 200 and video decoder 300may consider the neighboring block to be unavailable or may assume thatthe neighboring block has a default intra prediction mode. This mayavoid or reduce the need for video encoder 200 and video decoder 300 tostore mapping data to convert non-ALWIP directional intra predictionmodes to ALWIP modes. Avoiding or reducing the need to store suchmapping data may reduce the cost and complexity of video encoder 200 andvideo decoder 300.

In some examples, if a neighboring block is coded with combinedintra/inter mode (CIIP), the neighboring block may be considered asavailable and assigned the planar mode, or another appropriate non-ALWIPmode, for the MPM derivation of the ALWIP block. Alternatively, the CIIPmode may be mapped directly to an appropriate ALWIP mode to optimizecoding efficiency benefits. The assignment may depend on blockdimensions, etc. If the neighboring block is coded with intra block copymode (IBC), the block may be considered as available and assigned theplanar mode, or other appropriate non-ALWIP mode, for the MPM derivationof the ALWIP block. Alternatively, the IBC mode may be mapped directlyto an appropriate ALWIP mode to optimize coding efficiency benefits. Theassignment may depend on block dimensions, etc. Mapping CIIP modes andIBC modes directly (e.g., in a 1-to-1 relationship) to a particularmode, such as the planar mode, may avoid or reduce the need to storemore complex mapping data. Avoiding or reducing the need to store morecomplex mapping data may reduce the cost and complexity of video encoder200 and video decoder 300.

In accordance with a fifth technique of this disclosure, a constraintmay be introduced to disable ALWIP for blocks with width-to-height ratioof 4 or 0.25. In other words, a video coding standard may provide that ablock having a width-to-height ratio of 4 or 0.25 may not be coded usingALWIP. Not coding blocks having such width-to-height ratios may reducethe number of ALWIP parameters that video encoder 200 and video decoder300 may need to store, thereby potentially reducing the cost andcomplexity of video encoder 200 and video decoder 300.

The MPM list derivation for ALWIP uses the modes from neighboring blocksthat are adjacent to the top-right (e.g., just above the top-rightsample) and/or bottom-left samples (e.g., just left of the bottom-leftsample) of the current block. In some examples, the neighbor locationused to derive the MPMs for ALWIP is aligned with the neighbor locationused to derive the MPMs for regular intra prediction. More generally,any one or more blocks in the neighborhood of the current block may beused for the MPM derivation for ALWIP. FIG. 13 is a conceptual diagramillustrating example neighboring blocks 550, 552 used to derive ALWIPMPMs for a current block 554, in accordance with one or more techniquesof this disclosure. In the example of FIG. 13, block A (550) is a block(top-) adjacent to the top-right sample of current block 554. Block L(552) is a block (left-) adjacent to the bottom-left sample of currentblock 554.

The following specification text from JVET-N0217 is edited to implementthe techniques described with respect to the fourth technique of thisdisclosure. Changes are indicated by tags <!> . . . </!>.

Assigning Mode to CIIP Coded Block for MPM Derivation of ALWIP Block

Derivation Process for Affine Linear Weighted Intra Prediction Mode

Input to this process are:

-   -   a luma location (xCb, yCb) specifying the top-left sample of the        current luma coding block relative to the top-left luma sample        of the current picture,    -   a variable cbWidth specifying the width of the current coding        block in luma samples,    -   a variable cbHeight specifying the height of the current coding        block in luma samples.

In this process, the affine linear weighted intra prediction modeIntraPredModeY[xCb][yCb] is derived.

IntraPredModeY[xCb][yCb] is derived by the following ordered steps:

-   -   1. The neighboring locations (xNbA, yNbA) and (xNbB, yNbB) are        set equal to (xCb−1, yCb) and (xCb, yCb−1), respectively.    -   2. For X being replaced by either A or B, the variables        candLwipModeX are derived as follows:        -   The availability derivation process for a block as specified            in clause 6.4.X [Ed. (BB): Neighboring blocks availability            checking process tbd] is invoked with the location (xCurr,            yCurr) set equal to (xCb, yCb) and the neighboring location            (xNbY, yNbY) set equal to (xNbX, yNbX) as inputs, and the            output is assigned to availableX.        -   The candidate affine linear weighted intra prediction mode            candLwipModeX is derived as follows:            -   If one or more of the following conditions are true,                candLwipModeX is set equal to −1.                -   The variable availableX is equal to FALSE.                -   CuPredMode[xNbX][yNbX] is not equal to MODE INTRA                    and ciip_flag[xNbX][yNbX] is not equal to 1.                -   pcm_flag[xNbX][yNbX] is equal to 1.                -   X is equal to B and yCb−1 is less than                    ((yCb>>CtbLog2SizeY)<<CtbLog2SizeY).            -   Otherwise, the following applies:                -   The size type derivation process for a block as                    specified in clause 8.4.X.1 is invoked with the                    width of the current coding block in luma samples                    cbWidth and the height of the current coding block                    in luma samples cbHeight as input, and the output is                    assigned to variable sizeId.                -   If intra_lwip_flag[xNbX][yNbX] is equal to 1, the                    size type derivation process for a block as                    specified in clause 8.4.X.1 is invoked with the                    width of the neighboring coding block in luma                    samples nbWidthX and the height of the neighboring                    coding block in luma samples nbHeightX as input, and                    the output is assigned to variable sizeIdX.                -    If sizeId is equal to sizeIdX, candLwipModeX is set                    equal to IntraPredModeY[xNbX][yNbX].                -    Otherwise, candLwipModeX is set equal to −1.                -   <!>Otherwise, if intra_lwip_flag[xNbX][yNbX] is                    equal to 0 and ciip_flag ciip_flag[xNbX][yNbX] is                    equal to 1, IntraPredModeY[xNbX][yNbX] is set equal                    to INTRA_PLANAR and candLwipModeX is derived using                    IntraPredModeY[xNbX][yNbX] and sizeId as specified                    in Table 8-X1.</!>                -   Otherwise, candLwipModeX is derived using                    IntraPredModeY[xNbX][yNbX] and sizeId as specified                    in Table 8-X1.    -   3. The candLwipModeList[x] with x=0 . . . 2 is derived as        follows, using lwipMpmCand[sizeId] as specified in Table 8-X2:        -   If candLwipModeA and candLwipModeB are both equal to −1, the            following applies:            candLwipModeList[0]=lwipMpmCand[sizeId][0]  (8-X1)            candLwipModeList[1]=lwipMpmCand[sizeId][1]  (8-X2)            candLwipModeList[2]=lwipMpmCand[sizeId][2]  (8-X3)        -   Otherwise, the following applies:            -   If candLwipModeA is equal to candLwipModeB or if either                candLwipModeA or candLwipModeB is equal to −1, the                following applies:                candLwipModeList[0]=(candLwipModeA!=−1)?candLwipModeA:candLwipModeB                  (8-X4)                -   If candLwipModeList[0] is equal to                    lwipMpmCand[sizeId][0], the following applies:                    candLwipModeList[1]=lwipMpmCand[sizeId][1]  (8-X5)                    candLwipModeList[2]=lwipMpmCand[sizeId][2]  (8-X6)                -   Otherwise, the following applies:                    candLwipModeList[1]=lwipMpmCand[sizeId][0]  (8-X7)                    candLwipModeList[2]=(candLwipModeList[0]!=lwipMpmCand[sizeId][1])?lwipMpmCand[sizeId][1]:lwipMpmCand[sizeId][2]                      (8-X8)            -   Otherwise, the following applies:                candLwipModeList[0]=candLwipModeA   (8-X9)                candLwipModeList[1]=candLwipModeB   (8-X10)                -   If candLwipModeA and candLwipModeB are both not                    equal to lwipMpmCand[sizeId][0], the following                    applies:                    candLwipModeList[2]=lwipMpmCand[sizeId][0]  (8-X11)                -   Otherwise, the following applies:                -    If candLwipModeA and candLwipModeB are both not                    equal to lwipMpmCand[sizeId][1], the following                    applies:                    candLwipModeList[2]=lwipMpmCand[sizeId][1]  (8-X12)                -    Otherwise, the following applies:                    candLwipModeList[2]=lwipMpmCand[sizeId][2]  (8-X13)    -   4. IntraPredModeY[xCb][yCb] is derived by applying the following        procedure:        -   If intra_lwip_mpm_flag[xCb][yCb] is equal to 1, the            IntraPredModeY[xCb][yCb] is set equal to            candLwipModeList[intra_lwip_mpm_idx[xCb][yCb]].        -   Otherwise, IntraPredModeY[xCb][yCb] is derived by applying            the following ordered steps:            -   1. When candLwipModeList[i] is greater than                candLwipModeList[j] for i=0 . . . 1 and for each i,                j=(i+1) . . . 2, both values are swapped as follows:                (candLwipModeList[i],candLwipModeList[j])=Swap(candLwipModeList[i],candLwipModeList[j])  (8-X14)            -   2. IntraPredModeY[xCb][yCb] is derived by the following                ordered steps:                -   i. IntraPredModeY[xCb][yCb] is set equal to                    intra_lwip_mpm_remainder[xCb][yCb].                -   ii. For i equal to 0 to 2, inclusive, when                    IntraPredModeY[xCb][yCb] is greater than or equal to                    candLwipModeList[i], the value of                    IntraPredModeY[xCb][yCb] is incremented by one.

The variable IntraPredModeY[x][y] with x=xCb . . . xCb+cbWidth−1 andy=yCb . . . yCb+cbHeight−1 is set to be equal toIntraPredModeY[xCb][yCb].

8.4.X.1Derivation Process for Prediction Block Size Type

Input to this process are:

-   -   a variable cbWidth specifying the width of the current coding        block in luma samples,    -   a variable cbHeight specifying the height of the current coding        block in luma samples.        -   Output of this process is a variable sizeId.        -   The variable sizeId is derived as follows:    -   If both cbWidth and cbHeight are equal to 4, sizeId is set equal        to 0.    -   Otherwise, if both cbWidth and cbHeight are less than or equal        to 8, sizeId is set equal to 1.    -   Otherwise, sizeId is set equal to 2.

TABLE 8-X1 Specification of mapping between intra prediction and affinelinear weighted intra prediction modes IntraPredModeY block size typesizeId [xNbX][yNbX] 0 1 2  0 17 0 5  1 17 0 1 2, 3 17 10 3 4, 5 9 10 36, 7 9 10 3 8, 9 9 10 3 10, 11 9 10 0 12, 13 17 4 0 14, 15 17 6 0 16, 1717 7 4 18, 19 17 7 4 20, 21 17 7 4 22, 23 17 5 5 24, 25 17 5 1 26, 27 50 1 28, 29 5 0 1 30, 31 5 3 1 32, 33 5 3 1 34, 35 34 12 6 36, 37 22 12 638, 39 22 12 6 40, 41 22 12 6 42, 43 22 14 6 44, 45 34 14 10 46, 47 3414 10 48, 49 34 16 9 50, 51 34 16 9 52, 53 34 16 9 54, 55 34 15 9 56, 5734 13 9 58, 59 26 1 8 60, 61 26 1 8 62, 63 26 1 8 64, 65 26 1 8 66 26 18

TABLE 8-X2 Specification of affine linear weighted intra predictioncandidate modes candidate mode 0 1 2 lwipMpmCand[0] 17 34 5lwipMpmCand[1] 0 7 16 lwipMpmCand[2] 1 4 6

Example changes to the specification text of JVET-N0217 to implement thefifth technique of this disclosure are denoted with <!> . . . </!> tagsbelow.

Derivation Process for Affine Linear Weighted Intra Prediction Mode

Input to this process are:

-   -   a luma location (xCb, yCb) specifying the top-left sample of the        current luma coding block relative to the top-left luma sample        of the current picture,    -   a variable cbWidth specifying the width of the current coding        block in luma samples,    -   a variable cbHeight specifying the height of the current coding        block in luma samples.

In this process, the affine linear weighted intra prediction modeIntraPredModeY[xCb][yCb] is derived.

IntraPredModeY[xCb][yCb] is derived by the following ordered steps:

-   -   1. The neighboring locations (xNbA, yNbA) and (xNbB, yNbB) are        set equal to (xCb−1, yCb<!>+cbHeight−1</!>) and        (xCb<!>+cbWidth−1</!>, yCb−1), respectively.    -   2. For X being replaced by either A or B, the variables        candLwipModeX are derived as follows:        -   The availability derivation process for a block as specified            in clause 6.4.X [Ed. (BB): Neighboring blocks availability            checking process tbd] is invoked with the location (xCurr,            yCurr) set equal to (xCb, yCb) and the neighboring location            (xNbY, yNbY) set equal to (xNbX, yNbX) as inputs, and the            output is assigned to availableX.        -   The candidate affine linear weighted intra prediction mode            candLwipModeX is derived as follows:            -   If one or more of the following conditions are true,                candLwipModeX is set equal to −1.                -   The variable availableX is equal to FALSE.                -   CuPredMode[xNbX][yNbX] is not equal to MODE INTRA                    and ciip_flag[xNbX][yNbX] is not equal to 1.                -   pcm_flag[xNbX][yNbX] is equal to 1.                -   X is equal to B and yCb−1 is less than                    ((yCb>>CtbLog2SizeY)<<CtbLog2SizeY).            -   Otherwise, the following applies:                -   The size type derivation process for a block as                    specified in clause 8.4.X.1 is invoked with the                    width of the current coding block in luma samples                    cbWidth and the height of the current coding block                    in luma samples cbHeight as input, and the output is                    assigned to variable sizeId.                -   If intra_lwip_flag[xNbX][yNbX] is equal to 1, the                    size type derivation process for a block as                    specified in clause 8.4.X.1 is invoked with the                    width of the neighboring coding block in luma                    samples nbWidthX and the height of the neighboring                    coding block in luma samples nbHeightX as input, and                    the output is assigned to variable sizeIdX.                -    If sizeId is equal to sizeIdX, candLwipModeX is set                    equal to IntraPredModeY[xNbX][yNbX].                -    Otherwise, candLwipModeX is set equal to −1.                -   Otherwise, candLwipModeX is derived using                    IntraPredModeY[xNbX][yNbX] and sizeId as specified                    in Table 8-X1.    -   3. The candLwipModeList[x] with x=0 . . . 2 is derived as        follows, using lwipMpmCand[sizeId] as specified in Table 8-X2:        -   If candLwipModeA and candLwipModeB are both equal to −1, the            following applies:            candLwipModeList[0]=lwipMpmCand[sizeId][0]  (8-X1)            candLwipModeList[1]=lwipMpmCand[sizeId][1]  (8-X2)            candLwipModeList[2]=lwipMpmCand[sizeId][2]  (8-X3)        -   Otherwise, the following applies:            -   If candLwipModeA is equal to candLwipModeB or if either                candLwipModeA or candLwipModeB is equal to −1, the                following applies:                candLwipModeList[0]=(candLwipModeA!=−1)?candLwipModeA:candLwipModeB                  (8-X4)                -   If candLwipModeList[0] is equal to                    lwipMpmCand[sizeId][0], the following applies:                    candLwipModeList[1]=lwipMpmCand[sizeId][1]  (8-X5)                    candLwipModeList[2]=lwipMpmCand[sizeId][2]  (8-X6)                -   Otherwise, the following applies:                    candLwipModeList[1]=lwipMpmCand[sizeId][0]  (8-X7)                    candLwipModeList[2]=(candLwipModeList[0]!=lwipMpmCand[sizeId][1])?lwipMpmCand[sizeId][1]:lwipMpmCand[sizeId][2]                      (8-X8)            -   Otherwise, the following applies:                candLwipModeList[0]=candLwipModeA   (8-X9)                candLwipModeList[1]=candLwipModeB   (8-X10)                -   If candLwipModeA and candLwipModeB are both not                    equal to lwipMpmCand[sizeId][0], the following                    applies:                    candLwipModeList[2]=lwipMpmCand[sizeId][0]  (8-X11)                -   Otherwise, the following applies:                -    If candLwipModeA and candLwipModeB are both not                    equal to lwipMpmCand[sizeId][1], the following                    applies:                    candLwipModeList[2]=lwipMpmCand[sizeId][1]  (8-X12)                -    Otherwise, the following applies:                    candLwipModeList[2]=lwipMpmCand[sizeId][2]  (8-X13)    -   4. IntraPredModeY[xCb][yCb] is derived by applying the following        procedure:        -   If intra_lwip_mpm_flag[xCb][yCb] is equal to 1, the            IntraPredModeY[xCb][yCb] is set equal to            candLwipModeList[intra_lwip_mpm_idx[xCb][yCb]].        -   Otherwise, IntraPredModeY[xCb][yCb] is derived by applying            the following ordered steps:        -   1. When candLwipModeList[i] is greater than            candLwipModeList[j] for i=0 . . . 1 and for each i, j=(i+1)            . . . 2, both values are swapped as follows:            (candLwipModeList[i],candLwipModeList[j])=Swap(candLwipModeList[i],candLwipModeList[j])  (8-X14)        -   2. IntraPredModeY[xCb][yCb] is derived by the following            ordered steps:            -   i. IntraPredModeY[xCb][yCb] is set equal to                intra_lwip_mpm_remainder[xCb][yCb].            -   ii. For i equal to 0 to 2, inclusive, when                -   IntraPredModeY[xCb][yCb] is greater than or equal to                -   candLwipModeList[i], the value of                -   IntraPredModeY[xCb][yCb] is incremented by one.

The variable IntraPredModeY[x][y] with x=xCb . . . xCb+cbWidth−1 andy=yCb . . . yCb+cbHeight−1 is set to be equal toIntraPredModeY[xCb][yCb].

TABLE 8-X1 Specification of mapping between intra prediction and affinelinear weighted intra prediction modes IntraPredModeY block size typesizeId [xNbX][yNbX] 0 1 2  0 17 0 5  1 17 0 1 2, 3 17 10 3 4, 5 9 10 36, 7 9 10 3 8, 9 9 10 3 10, 11 9 10 0 12, 13 17 4 0 14, 15 17 6 0 16, 1717 7 4 18, 19 17 7 4 20, 21 17 7 4 22, 23 17 5 5 24, 25 17 5 1 26, 27 50 1 28, 29 5 0 1 30, 31 5 3 1 32, 33 5 3 1 34, 35 34 12 6 36, 37 22 12 638, 39 22 12 6 40, 41 22 12 6 42, 43 22 14 6 44, 45 34 14 10 46, 47 3414 10 48, 49 34 16 9 50, 51 34 16 9 52, 53 34 16 9 54, 55 34 15 9 56, 5734 13 9 58, 59 26 1 8 60, 61 26 1 8 62, 63 26 1 8 64, 65 26 1 8 66 26 18

TABLE 8-X2 Specification of affine linear weighted intra predictioncandidate modes candidate mode 0 1 2 lwipMpmCand[0] 17 34 5lwipMpmCand[1] 0 7 16 lwipMpmCand[2] 1 4 6

This disclosure may generally refer to “signaling” certain information,such as syntax elements. The term “signaling” may generally refer to thecommunication of values for syntax elements and/or other data used todecode encoded video data. That is, video encoder 200 may signal valuesfor syntax elements in the bitstream. In general, signaling refers togenerating a value in the bitstream. As noted above, source device 102may transport the bitstream to destination device 116 substantially inreal time, or not in real time, such as might occur when storing syntaxelements to storage device 112 for later retrieval by destination device116.

FIGS. 14A and 14B are conceptual diagrams illustrating an examplequadtree binary tree (QTBT) structure 130, and a corresponding codingtree unit (CTU) 132. The solid lines represent quadtree splitting, anddotted lines indicate binary tree splitting. In each split (i.e.,non-leaf) node of the binary tree, one flag is signaled to indicatewhich splitting type (i.e., horizontal or vertical) is used, where 0indicates horizontal splitting and 1 indicates vertical splitting inthis example. For the quadtree splitting, there is no need to indicatethe splitting type, since quadtree nodes split a block horizontally andvertically into 4 sub-blocks with equal size. Accordingly, video encoder200 may encode, and video decoder 300 may decode, syntax elements (suchas splitting information) for a region tree level (i.e., the firstlevel) of QTBT structure 130 (i.e., the solid lines) and syntax elements(such as splitting information) for a prediction tree level (i.e., thesecond level) of QTBT structure 130 (i.e., the dashed lines). Videoencoder 200 may encode, and video decoder 300 may decode, video data,such as prediction and transform data, for CUs represented by terminalleaf nodes of QTBT structure 130.

In general, CTU 132 of FIG. 14B may be associated with parametersdefining sizes of blocks corresponding to nodes of QTBT structure 130 atthe first and second levels. These parameters may include a CTU size(representing a size of CTU 132 in samples), a minimum quadtree size(MinQTSize, representing a minimum allowed quadtree leaf node size), amaximum binary tree size (MaxBTSize, representing a maximum allowedbinary tree root node size), a maximum binary tree depth (MaxBTDepth,representing a maximum allowed binary tree depth), and a minimum binarytree size (MinBTSize, representing the minimum allowed binary tree leafnode size).

The root node of a QTBT structure corresponding to a CTU may have fourchild nodes at the first level of the QTBT structure, each of which maybe partitioned according to quadtree partitioning. That is, nodes of thefirst level are either leaf nodes (having no child nodes) or have fourchild nodes. The example of QTBT structure 130 represents such nodes asincluding the parent node and child nodes having solid lines forbranches. If nodes of the first level are not larger than the maximumallowed binary tree root node size (MaxBTSize), they can be furtherpartitioned by respective binary trees. The binary tree splitting of onenode can be iterated until the nodes resulting from the split reach theminimum allowed binary tree leaf node size (MinBTSize) or the maximumallowed binary tree depth (MaxBTDepth). The example of QTBT structure130 represents such nodes as having dashed lines for branches. Thebinary tree leaf node is referred to as a coding unit (CU), which isused for prediction (e.g., intra-picture or inter-picture prediction)and transform, without any further partitioning. As discussed above, CUsmay also be referred to as “video blocks” or “blocks.”

In one example of the QTBT partitioning structure, the CTU size is setas 128×128 (luma samples and two corresponding 64×64 chroma samples),the MinQTSize is set as 16×16, the MaxBTSize is set as 64×64, theMinBTSize (for both width and height) is set as 4, and the MaxBTDepth isset as 4. The quadtree partitioning is applied to the CTU first togenerate quad-tree leaf nodes. The quadtree leaf nodes may have sizesfrom 16×16 (i.e., the MinQTSize) to 128×128 (i.e., the CTU size). If thequadtree leaf node is 128×128, it will not be further split by thebinary tree, since the size exceeds the MaxBTSize (i.e., 64×64, in thisexample). Otherwise, the quadtree leaf node will be further partitionedby the binary tree. Therefore, the quadtree leaf node is also the rootnode for the binary tree and has a binary tree depth as 0. When thebinary tree depth reaches MaxBTDepth (4, in this example), no furthersplitting is permitted. When the binary tree node has width equal toMinBTSize (4, in this example), it implies that no further verticalsplitting is permitted. Similarly, a binary tree node having a heightequal to MinBTSize that implies no further horizontal splitting ispermitted for that binary tree node. As noted above, leaf nodes of thebinary tree are referred to as CUs and are further processed accordingto prediction and transform without further partitioning.

FIG. 15 is a block diagram illustrating an example video encoder 200that may perform the techniques of this disclosure. FIG. 15 is providedfor purposes of explanation and should not be considered limiting of thetechniques as broadly exemplified and described in this disclosure. Forpurposes of explanation, this disclosure describes video encoder 200 inthe context of video coding standards such as the HEVC video codingstandard and the H.266 video coding standard in development. However,the techniques of this disclosure are not limited to these video codingstandards and are applicable generally to video encoding and decoding.

In the example of FIG. 15, video encoder 200 includes video data memory230, mode selection unit 202, residual generation unit 204, transformprocessing unit 206, quantization unit 208, inverse quantization unit210, inverse transform processing unit 212, reconstruction unit 214,filter unit 216, decoded picture buffer (DPB) 218, and entropy encodingunit 220. Any or all of video data memory 230, mode selection unit 202,residual generation unit 204, transform processing unit 206,quantization unit 208, inverse quantization unit 210, inverse transformprocessing unit 212, reconstruction unit 214, filter unit 216, DPB 218,and entropy encoding unit 220 may be implemented in one or moreprocessors or in processing circuitry. Moreover, video encoder 200 mayinclude additional or alternative processors or processing circuitry toperform these and other functions.

Video data memory 230 may store video data to be encoded by thecomponents of video encoder 200. Video encoder 200 may receive the videodata stored in video data memory 230 from, for example, video source 104(FIG. 1). DPB 218 may act as a reference picture memory that storesreference video data for use in prediction of subsequent video data byvideo encoder 200. Video data memory 230 and DPB 218 may be formed byany of a variety of memory devices, such as dynamic random access memory(DRAM), including synchronous DRAM (SDRAM), magnetoresistive RAM (MRAM),resistive RAM (RRAM), or other types of memory devices. Video datamemory 230 and DPB 218 may be provided by the same memory device orseparate memory devices. In various examples, video data memory 230 maybe on-chip with other components of video encoder 200, as illustrated,or off-chip relative to those components.

In this disclosure, reference to video data memory 230 should not beinterpreted as being limited to memory internal to video encoder 200,unless specifically described as such, or memory external to videoencoder 200, unless specifically described as such. Rather, reference tovideo data memory 230 should be understood as reference memory thatstores video data that video encoder 200 receives for encoding (e.g.,video data for a current block that is to be encoded). Memory 106 ofFIG. 1 may also provide temporary storage of outputs from the variousunits of video encoder 200.

The various units of FIG. 15 are illustrated to assist withunderstanding the operations performed by video encoder 200. The unitsmay be implemented as fixed-function circuits, programmable circuits, ora combination thereof. Fixed-function circuits refer to circuits thatprovide particular functionality and are preset on the operations thatcan be performed. Programmable circuits refer to circuits that can beprogrammed to perform various tasks and provide flexible functionalityin the operations that can be performed. For instance, programmablecircuits may execute software or firmware that cause the programmablecircuits to operate in the manner defined by instructions of thesoftware or firmware. Fixed-function circuits may execute softwareinstructions (e.g., to receive parameters or output parameters), but thetypes of operations that the fixed-function circuits perform aregenerally immutable. In some examples, one or more of the units may bedistinct circuit blocks (fixed-function or programmable), and in someexamples, the one or more units may be integrated circuits.

Video encoder 200 may include arithmetic logic units (ALUs), elementaryfunction units (EFUs), digital circuits, analog circuits, and/orprogrammable cores, formed from programmable circuits. In examples wherethe operations of video encoder 200 are performed using softwareexecuted by the programmable circuits, memory 106 (FIG. 1) may store theobject code of the software that video encoder 200 receives andexecutes, or another memory within video encoder 200 (not shown) maystore such instructions.

Video data memory 230 is configured to store received video data. Videoencoder 200 may retrieve a picture of the video data from video datamemory 230 and provide the video data to residual generation unit 204and mode selection unit 202. Video data in video data memory 230 may beraw video data that is to be encoded.

Mode selection unit 202 includes a motion estimation unit 222, motioncompensation unit 224, and an intra-prediction unit 226. Mode selectionunit 202 may include additional functional units to perform videoprediction in accordance with other prediction modes. As examples, modeselection unit 202 may include a palette unit, an intra-block copy unit(which may be part of motion estimation unit 222 and/or motioncompensation unit 224), an affine unit, a linear model (LM) unit, or thelike. For instance, in the example of FIG. 15, intra-prediction unit 226includes an ALWIP unit 227 configured to perform ALWIP.

Mode selection unit 202 generally coordinates multiple encoding passesto test combinations of encoding parameters and resultingrate-distortion values for such combinations. The encoding parametersmay include partitioning of CTUs into CUs, prediction modes for the CUs,transform types for residual data of the CUs, quantization parametersfor residual data of the CUs, and so on. Mode selection unit 202 mayultimately select the combination of encoding parameters havingrate-distortion values that are better than the other testedcombinations.

Video encoder 200 may partition a picture retrieved from video datamemory 230 into a series of CTUs, and encapsulate one or more CTUswithin a slice. Mode selection unit 202 may partition a CTU of thepicture in accordance with a tree structure, such as the QTBT structureor the quad-tree structure of HEVC described above. As described above,video encoder 200 may form one or more CUs from partitioning a CTUaccording to the tree structure. Such a CU may also be referred togenerally as a “video block” or “block.”

In general, mode selection unit 202 also controls the components thereof(e.g., motion estimation unit 222, motion compensation unit 224, andintra-prediction unit 226) to generate a prediction block for a currentblock (e.g., a current CU, or in HEVC, the overlapping portion of a PUand a TU). For inter-prediction of a current block, motion estimationunit 222 may perform a motion search to identify one or more closelymatching reference blocks in one or more reference pictures (e.g., oneor more previously coded pictures stored in DPB 218). In particular,motion estimation unit 222 may calculate a value representative of howsimilar a potential reference block is to the current block, e.g.,according to sum of absolute difference (SAD), sum of squareddifferences (SSD), mean absolute difference (MAD), mean squareddifferences (MSD), or the like. Motion estimation unit 222 may generallyperform these calculations using sample-by-sample differences betweenthe current block and the reference block being considered. Motionestimation unit 222 may identify a reference block having a lowest valueresulting from these calculations, indicating a reference block thatmost closely matches the current block.

Motion estimation unit 222 may form one or more motion vectors (MVs)that define the positions of the reference blocks in the referencepictures relative to the position of the current block in a currentpicture. Motion estimation unit 222 may then provide the motion vectorsto motion compensation unit 224. For example, for uni-directionalinter-prediction, motion estimation unit 222 may provide a single motionvector, whereas for bi-directional inter-prediction, motion estimationunit 222 may provide two motion vectors. Motion compensation unit 224may then generate a prediction block using the motion vectors. Forexample, motion compensation unit 224 may retrieve data of the referenceblock using the motion vector. As another example, if the motion vectorhas fractional sample precision, motion compensation unit 224 mayinterpolate values for the prediction block according to one or moreinterpolation filters. Moreover, for bi-directional inter-prediction,motion compensation unit 224 may retrieve data for two reference blocksidentified by respective motion vectors and combine the retrieved data,e.g., through sample-by-sample averaging or weighted averaging.

As another example, for intra-prediction, or intra-prediction coding,intra-prediction unit 226 may generate the prediction block from samplesneighboring the current block. For example, for directional modes,intra-prediction unit 226 may generally mathematically combine values ofneighboring samples and populate these calculated values in the defineddirection across the current block to produce the prediction block. Asanother example, for DC mode, intra-prediction unit 226 may calculate anaverage of the neighboring samples to the current block and generate theprediction block to include this resulting average for each sample ofthe prediction block.

In accordance with one example of the third technique of thisdisclosure, intra-prediction unit 226 may perform an MPM derivationprocess that derives one or more MPMs for a current block of the videodata. In this example, the current block is not coded using ALWIP. Aspart of performing the MPM derivation process, intra-prediction unit 226may determine whether a neighboring block of the current block is anALWIP-coded neighboring block. Based on the neighboring block being anALWIP-coded neighboring block, intra-prediction unit 226 may determinethat a value of an intra prediction mode of the neighboring block is adefault value, such as a value corresponding to a planar mode.Intra-prediction unit 226 may include an intra prediction modecorresponding to the default value as one of the one or more MPMs. Videoencoder 200 may encode the current block based on one of the MPMs forthe current block or another intra prediction mode. For instance, aspart of video encoder 200 encoding the current block, intra-predictionunit 226 may use one of the MPMs or another intra prediction mode togenerate a prediction block for the current block.

Mode selection unit 202 provides the prediction block to residualgeneration unit 204. Residual generation unit 204 receives a raw,unencoded version of the current block from video data memory 230 andthe prediction block from mode selection unit 202. Residual generationunit 204 calculates sample-by-sample differences between the currentblock and the prediction block. The resulting sample-by-sampledifferences define a residual block for the current block. In someexamples, residual generation unit 204 may also determine differencesbetween sample values in the residual block to generate a residual blockusing residual differential pulse code modulation (RDPCM). In someexamples, residual generation unit 204 may be formed using one or moresubtractor circuits that perform binary subtraction.

In examples where mode selection unit 202 partitions CUs into PUs, eachPU may be associated with a luma PU and corresponding chroma PUs. Videoencoder 200 and video decoder 300 may support PUs having various sizes.As indicated above, the size of a CU may refer to the size of the lumacoding block of the CU and the size of a PU may refer to the size of aluma prediction unit of the PU. Assuming that the size of a particularCU is 2N×2N, video encoder 200 may support PU sizes of 2N×2N or N×N forintra prediction, and symmetric PU sizes of 2N×2N, 2N×N, N×2N, N×N, orsimilar for inter prediction. Video encoder 200 and video decoder 300may also support asymmetric partitioning for PU sizes of 2NxnU, 2NxnD,nLx2N, and nRx2N for inter prediction.

In examples where mode selection unit does not further partition a CUinto PUs, each CU may be associated with a luma coding block andcorresponding chroma coding blocks. As above, the size of a CU may referto the size of the luma coding block of the CU. The video encoder 200and video decoder 300 may support CU sizes of 2N×2N, 2N×N, or N×2N.

For other video coding techniques such as an intra-block copy modecoding, an affine-mode coding, and linear model (LM) mode coding, as afew examples, mode selection unit 202, via respective units associatedwith the coding techniques, generates a prediction block for the currentblock being encoded. In some examples, such as palette mode coding, modeselection unit 202 may not generate a prediction block, and insteadgenerate syntax elements that indicate the manner in which toreconstruct the block based on a selected palette. In such modes, modeselection unit 202 may provide these syntax elements to entropy encodingunit 220 to be encoded.

As described above, residual generation unit 204 receives the video datafor the current block and the corresponding prediction block. Residualgeneration unit 204 then generates a residual block for the currentblock. To generate the residual block, residual generation unit 204calculates sample-by-sample differences between the prediction block andthe current block.

Transform processing unit 206 applies one or more transforms to theresidual block to generate a block of transform coefficients (referredto herein as a “transform coefficient block”). Transform processing unit206 may apply various transforms to a residual block to form thetransform coefficient block. For example, transform processing unit 206may apply a discrete cosine transform (DCT), a directional transform, aKarhunen-Loeve transform (KLT), or a conceptually similar transform to aresidual block. In some examples, transform processing unit 206 mayapply multiple transforms to a residual block, e.g., a primary transformand a secondary transform, such as a rotational transform. In someexamples, transform processing unit 206 does not apply transforms to aresidual block.

Quantization unit 208 may quantize the transform coefficients in atransform coefficient block, to produce a quantized transformcoefficient block. Quantization unit 208 may quantize transformcoefficients of a transform coefficient block according to aquantization parameter (QP) value associated with the current block.Video encoder 200 (e.g., via mode selection unit 202) may adjust thedegree of quantization applied to the transform coefficient blocksassociated with the current block by adjusting the QP value associatedwith the CU. Quantization may introduce loss of information, and thus,quantized transform coefficients may have lower precision than theoriginal transform coefficients produced by transform processing unit206.

Inverse quantization unit 210 and inverse transform processing unit 212may apply inverse quantization and inverse transforms to a quantizedtransform coefficient block, respectively, to reconstruct a residualblock from the transform coefficient block. Reconstruction unit 214 mayproduce a reconstructed block corresponding to the current block (albeitpotentially with some degree of distortion) based on the reconstructedresidual block and a prediction block generated by mode selection unit202. For example, reconstruction unit 214 may add samples of thereconstructed residual block to corresponding samples from theprediction block generated by mode selection unit 202 to produce thereconstructed block.

Filter unit 216 may perform one or more filter operations onreconstructed blocks. For example, filter unit 216 may performdeblocking operations to reduce blockiness artifacts along edges of CUs.Operations of filter unit 216 may be skipped, in some examples.

Video encoder 200 stores reconstructed blocks in DPB 218. For instance,in examples where operations of filter unit 312 are not performed,reconstruction unit 310 may store reconstructed blocks to DPB 314. Inexamples where operations of filter unit 312 are performed, filter unit312 may store the filtered reconstructed blocks to DPB 314. Forinstance, in examples where operations of filter unit 216 are notneeded, reconstruction unit 214 may store reconstructed blocks to DPB218. In examples where operations of filter unit 216 are needed, filterunit 216 may store the filtered reconstructed blocks to DPB 218. Motionestimation unit 222 and motion compensation unit 224 may retrieve areference picture from DPB 218, formed from the reconstructed (andpotentially filtered) blocks, to inter-predict blocks of subsequentlyencoded pictures. In addition, intra-prediction unit 226 may usereconstructed blocks in DPB 218 of a current picture to intra-predictother blocks in the current picture.

In general, entropy encoding unit 220 may entropy encode syntax elementsreceived from other functional components of video encoder 200. Forexample, entropy encoding unit 220 may entropy encode quantizedtransform coefficient blocks from quantization unit 208. As anotherexample, entropy encoding unit 220 may entropy encode prediction syntaxelements (e.g., motion information for inter-prediction or intra-modeinformation for intra-prediction) from mode selection unit 202. Entropyencoding unit 220 may perform one or more entropy encoding operations onthe syntax elements, which are another example of video data, togenerate entropy-encoded data. For example, entropy encoding unit 220may perform a context-adaptive variable length coding (CAVLC) operation,a CABAC operation, a variable-to-variable (V2V) length coding operation,a syntax-based context-adaptive binary arithmetic coding (SBAC)operation, a Probability Interval Partitioning Entropy (PIPE) codingoperation, an Exponential-Golomb encoding operation, or another type ofentropy encoding operation on the data. In some examples, entropyencoding unit 220 may operate in bypass mode where syntax elements arenot entropy encoded.

Video encoder 200 may output a bitstream that includes the entropyencoded syntax elements needed to reconstruct blocks of a slice orpicture. In particular, entropy encoding unit 220 may output thebitstream.

The operations described above are described with respect to a block.Such description should be understood as being operations for a lumacoding block and/or chroma coding blocks. As described above, in someexamples, the luma coding block and chroma coding blocks are luma andchroma components of a CU. In some examples, the luma coding block andthe chroma coding blocks are luma and chroma components of a PU.

In some examples, operations performed with respect to a luma codingblock need not be repeated for the chroma coding blocks. As one example,operations to identify a motion vector (MV) and reference picture for aluma coding block need not be repeated for identifying an MV andreference picture for the chroma blocks. Rather, the MV for the lumacoding block may be scaled to determine the MV for the chroma blocks,and the reference picture may be the same. As another example, theintra-prediction process may be the same for the luma coding blocks andthe chroma coding blocks.

Video encoder 200 represents an example of a device configured to encodevideo data including a memory configured to store video data, and one ormore processing units implemented in circuitry and configured to performthe ALWIP techniques of this disclosure. For instance, video encoder 200may represent an example of a device including a memory configured tostore video data and one or more processing units implemented incircuitry and configured to perform a MPM derivation process thatderives one or more MPMs for a current block of the video data, whereinthe current block is not coded using ALWIP. In this example, the one ormore processors are configured such that, as part of performing the MPMderivation process, the one or more processors determine whether aneighboring block of the current block is an ALWIP-coded neighboringblock. Furthermore, the one or more processors are configured to, basedon the neighboring block being an ALWIP-coded neighboring block,determine that a value of an intra prediction mode of the neighboringblock is a default value, such as a value corresponding to a planarmode. The one or more processors may further be configured to include anintra prediction mode corresponding to the default value as one of theone or more MPMs. The one or more processors may encode the currentblock based on one of the MPMs for the current block.

Furthermore, in some examples where a block is a chroma block coded witha DM mode, video encoder 200 represents an example of a device thatincludes a memory configured to store video data and one or moreprocessors configured to determine whether a collocated luma block iscoded with ALWIP. In such examples, the collocated luma block iscollocated with the block. Furthermore, in such examples, the one ormore processors may, based on the collocated luma block being coded withALWIP, determine, e.g., infer, that an intra prediction mode of thecollocated luma block is a default value. In other words, the one ormore processors may determine or otherwise treat the intra predictionmode of the collocated luma block as being a default intra predictionmode, such as the planar intra prediction mode. The one or moreprocessors may be configured to encode the block using an intraprediction mode corresponding to the default value.

FIG. 16 is a block diagram illustrating an example video decoder 300that may perform the techniques of this disclosure. FIG. 16 is providedfor purposes of explanation and is not limiting on the techniques asbroadly exemplified and described in this disclosure. For purposes ofexplanation, this disclosure describes video decoder 300 according tothe techniques of JEM, VVC, and HEVC. However, the techniques of thisdisclosure may be performed by video coding devices that are configuredto other video coding standards.

In the example of FIG. 16, video decoder 300 includes coded picturebuffer (CPB) memory 320, entropy decoding unit 302, predictionprocessing unit 304, inverse quantization unit 306, inverse transformprocessing unit 308, reconstruction unit 310, filter unit 312, anddecoded picture buffer (DPB) 314. Any or all of CPB memory 320, entropydecoding unit 302, prediction processing unit 304, inverse quantizationunit 306, inverse transform processing unit 308, reconstruction unit310, filter unit 312, and DPB 314 may be implemented in one or moreprocessors or in processing circuitry. Moreover, video decoder 300 mayinclude additional or alternative processors or processing circuitry toperform these and other functions.

Prediction processing unit 304 includes motion compensation unit 316 andintra-prediction unit 318. Prediction processing unit 304 may includeadditional units to perform prediction in accordance with otherprediction modes. As examples, prediction processing unit 304 mayinclude a palette unit, an intra-block copy unit (which may form part ofmotion compensation unit 316), an affine unit, a linear model (LM) unit,or the like. For instance, in the example of FIG. 16, intra-predictionunit 318 includes an ALWIP unit 319 that performs an ALWIP process. Inother examples, video decoder 300 may include more, fewer, or differentfunctional components.

CPB memory 320 may store video data, such as an encoded video bitstream,to be decoded by the components of video decoder 300. The video datastored in CPB memory 320 may be obtained, for example, fromcomputer-readable medium 110 (FIG. 1). CPB memory 320 may include a CPBthat stores encoded video data (e.g., syntax elements) from an encodedvideo bitstream. Also, CPB memory 320 may store video data other thansyntax elements of a coded picture, such as temporary data representingoutputs from the various units of video decoder 300. DPB 314 generallystores decoded pictures, which video decoder 300 may output and/or useas reference video data when decoding subsequent data or pictures of theencoded video bitstream. CPB memory 320 and DPB 314 may be formed by anyof a variety of memory devices, such as dynamic random access memory(DRAM), including synchronous DRAM (SDRAM), magnetoresistive RAM (MRAM),resistive RAM (RRAM), or other types of memory devices. CPB memory 320and DPB 314 may be provided by the same memory device or separate memorydevices. In various examples, CPB memory 320 may be on-chip with othercomponents of video decoder 300, or off-chip relative to thosecomponents.

Additionally or alternatively, in some examples, video decoder 300 mayretrieve coded video data from memory 120 (FIG. 1). That is, memory 120may store data as discussed above with CPB memory 320. Likewise, memory120 may store instructions to be executed by video decoder 300, whensome or all of the functionality of video decoder 300 is implemented insoftware to be executed by processing circuitry of video decoder 300.

The various units shown in FIG. 16 are illustrated to assist withunderstanding the operations performed by video decoder 300. The unitsmay be implemented as fixed-function circuits, programmable circuits, ora combination thereof. Similar to FIG. 15, fixed-function circuits referto circuits that provide particular functionality, and are preset on theoperations that can be performed. Programmable circuits refer tocircuits that can be programmed to perform various tasks and provideflexible functionality in the operations that can be performed. Forinstance, programmable circuits may execute software or firmware thatcause the programmable circuits to operate in the manner defined byinstructions of the software or firmware. Fixed-function circuits mayexecute software instructions (e.g., to receive parameters or outputparameters), but the types of operations that the fixed-functioncircuits perform are generally immutable. In some examples, one or moreof the units may be distinct circuit blocks (fixed-function orprogrammable), and in some examples, the one or more units may beintegrated circuits.

Video decoder 300 may include ALUs, EFUs, digital circuits, analogcircuits, and/or programmable cores formed from programmable circuits.In examples where the operations of video decoder 300 are performed bysoftware executing on the programmable circuits, on-chip or off-chipmemory may store instructions (e.g., object code) of the software thatvideo decoder 300 receives and executes.

Entropy decoding unit 302 may receive encoded video data from the CPBand entropy decode the video data to reproduce syntax elements.Prediction processing unit 304, inverse quantization unit 306, inversetransform processing unit 308, reconstruction unit 310, and filter unit312 may generate decoded video data based on the syntax elementsextracted from the bitstream.

In general, video decoder 300 reconstructs a picture on a block-by-blockbasis. Video decoder 300 may perform a reconstruction operation on eachblock individually (where the block currently being reconstructed, i.e.,decoded, may be referred to as a “current block”).

Entropy decoding unit 302 may entropy decode syntax elements definingquantized transform coefficients of a quantized transform coefficientblock, as well as transform information, such as a quantizationparameter (QP) and/or transform mode indication(s). Inverse quantizationunit 306 may use the QP associated with the quantized transformcoefficient block to determine a degree of quantization and, likewise, adegree of inverse quantization for inverse quantization unit 306 toapply. Inverse quantization unit 306 may, for example, perform a bitwiseleft-shift operation to inverse quantize the quantized transformcoefficients. Inverse quantization unit 306 may thereby form a transformcoefficient block including transform coefficients.

After inverse quantization unit 306 forms the transform coefficientblock, inverse transform processing unit 308 may apply one or moreinverse transforms to the transform coefficient block to generate aresidual block associated with the current block. For example, inversetransform processing unit 308 may apply an inverse DCT, an inverseinteger transform, an inverse Karhunen-Loeve transform (KLT), an inverserotational transform, an inverse directional transform, or anotherinverse transform to the transform coefficient block.

Furthermore, prediction processing unit 304 generates a prediction blockaccording to prediction information syntax elements that were entropydecoded by entropy decoding unit 302. For example, if the predictioninformation syntax elements indicate that the current block isinter-predicted, motion compensation unit 316 may generate theprediction block. In this case, the prediction information syntaxelements may indicate a reference picture in DPB 314 from which toretrieve a reference block, as well as a motion vector identifying alocation of the reference block in the reference picture relative to thelocation of the current block in the current picture. Motioncompensation unit 316 may generally perform the inter-prediction processin a manner that is substantially similar to that described with respectto motion compensation unit 224 (FIG. 15).

As another example, if the prediction information syntax elementsindicate that the current block is intra-predicted, intra-predictionunit 318 may generate the prediction block according to anintra-prediction mode indicated by the prediction information syntaxelements. Again, intra-prediction unit 318 may generally perform theintra-prediction process in a manner that is substantially similar tothat described with respect to intra-prediction unit 226 (FIG. 15).Intra-prediction unit 318 may retrieve data of neighboring samples tothe current block from DPB 314.

In accordance with one example of the third technique of thisdisclosure, intra-prediction unit 318 may perform an MPM derivationprocess that derives one or more MPMs for a current block of the videodata. In this example, the current block is not coded using ALWIP. Aspart of performing the MPM derivation process, intra-prediction unit 318may determine whether a neighboring block of the current block is anALWIP-coded neighboring block. Based on the neighboring block being anALWIP-coded neighboring block, intra-prediction unit 318 may determinethat a value of an intra prediction mode of the neighboring block is adefault value, such as a value corresponding to a planar mode.Intra-prediction unit 318 may include an intra prediction modecorresponding to the default value as one of the one or more MPMs. Videodecoder 300 may decode the current block based on one of the MPMs forthe current block or another intra prediction mode. For instance, aspart of video decoder 300 coding the current block, intra-predictionunit 318 may use one of the MPMs or another intra prediction mode togenerate a prediction block for the current block.

Reconstruction unit 310 may reconstruct the current block using theprediction block and the residual block. For example, reconstructionunit 310 may add samples of the residual block to corresponding samplesof the prediction block to reconstruct the current block.

Filter unit 312 may perform one or more filter operations onreconstructed blocks. For example, filter unit 312 may performdeblocking operations to reduce blockiness artifacts along edges of thereconstructed blocks. Operations of filter unit 312 are not necessarilyperformed in all examples.

Video decoder 300 may store the reconstructed blocks in DPB 314. Asdiscussed above, DPB 314 may provide reference information, such assamples of a current picture for intra-prediction and previously decodedpictures for subsequent motion compensation, to prediction processingunit 304. Moreover, video decoder 300 may output decoded pictures fromDPB for subsequent presentation on a display device, such as displaydevice 118 of FIG. 1.

In this manner, video decoder 300 represents an example of a videodecoding device including a memory configured to store video data, andone or more processing units implemented in circuitry and configured toperform the ALWIP techniques of this disclosure. For instance, videodecoder 300 may represent an example of a device including a memoryconfigured to store video data and one or more processing unitsimplemented in circuitry and configured to perform a MPM derivationprocess that derives one or more MPMs for a current block of the videodata, wherein the current block is not coded using ALWIP. In thisexample, the one or more processors are configured such that, as part ofperforming the MPM derivation process, the one or more processorsdetermine whether a neighboring block of the current block is anALWIP-coded neighboring block. Furthermore, the one or more processorsare configured to, based on the neighboring block being an ALWIP-codedneighboring block, determine that a value of an intra prediction mode ofthe neighboring block is a default value, such as a value correspondingto a planar mode. The one or more processors may include an intraprediction mode corresponding to the default as one of the one or moreMPMs. The one or more processors may decode the current block based onone of the MPMs for the current block.

Furthermore, in some examples where a block is a chroma block coded witha DM mode, video encoder 200 represents an example of a device thatincludes a memory configured to store video data and one or moreprocessors configured to determine whether a collocated luma block iscoded with ALWIP. In such examples, the collocated luma block iscollocated with the block. Furthermore, in such examples, the one ormore processors may, based on the collocated luma block being coded withALWIP, determine, e.g., infer, that an intra prediction mode of thecollocated luma block is a default value. In other words, the one ormore processors may determine or otherwise treat the intra predictionmode of the collocated luma block as being a default intra predictionmode, such as the planar intra prediction mode. The one or moreprocessors may be configured to decode the block using an intraprediction mode corresponding to the default value.

FIG. 17 is a flowchart illustrating an example method for encoding acurrent block. The current block may include a current CU. Althoughdescribed with respect to video encoder 200 (FIGS. 1 and 15), it shouldbe understood that other devices may be configured to perform a methodsimilar to that of FIG. 17.

In this example, video encoder 200 initially predicts the current block(350). For example, video encoder 200 may form a prediction block forthe current block. In some examples, video encoder 200 (e.g.,intra-prediction unit 226 of video encoder 200) perform an MPMderivation process that derives one or more MPMs for the current block.In this example, the current block is not coded using ALWIP. The MPMsmay include intra prediction modes and, in some examples, each of theMPMs is an intra prediction mode. Furthermore, in this example, as partof performing the MPM derivation process, video encoder 200 maydetermine whether a neighboring block of the current block is anALWIP-coded neighboring block and, based on the neighboring block beingan ALWIP-coded neighboring block, determine that a value of an intraprediction mode of the neighboring block is a default value. Videoencoder 200 may include an intra prediction mode corresponding to thedefault value as one of the one or more MPMs. Video encoder 200 may thenuse one of the MPMs or another intra prediction mode to form theprediction block for the current block.

Video encoder 200 may then calculate a residual block for the currentblock (352). To calculate the residual block, video encoder 200 maycalculate a difference between the original, unencoded block and theprediction block for the current block. Video encoder 200 may thentransform and quantize transform coefficients of the residual block(354).

Next, video encoder 200 may scan the quantized transform coefficients ofthe residual block (356). During the scan, or following the scan, videoencoder 200 may entropy encode the transform coefficients (358). Forexample, video encoder 200 may encode the transform coefficients usingCAVLC or CABAC. Video encoder 200 may then output the entropy encodeddata of the block (360).

FIG. 18 is a flowchart illustrating an example method for decoding acurrent block of video data. The current block may include a current CU.Although described with respect to video decoder 300 (FIGS. 1 and 16),it should be understood that other devices may be configured to performa method similar to that of FIG. 18.

Video decoder 300 may receive entropy coded data for the current block,such as entropy coded prediction information and entropy coded data fortransform coefficients of a residual block corresponding to the currentblock (370). Video decoder 300 may entropy decode the entropy coded datato determine prediction information for the current block and toreproduce transform coefficients of the residual block (372).

Video decoder 300 may predict the current block (374), e.g., using anintra- or inter-prediction mode as indicated by the predictioninformation for the current block, to calculate a prediction block forthe current block. In some examples, video decoder 300 (e.g.,intra-prediction unit 318 of video decoder 300) perform an MPMderivation process that derives one or more MPMs for the current block.In this example, the current block is not coded using ALWIP. The MPMsmay include intra prediction modes and, in some examples, each of theMPMs is an intra prediction mode. Furthermore, in this example, as partof performing the MPM derivation process, video decoder 300 maydetermine whether a neighboring block of the current block is anALWIP-coded neighboring block and, based on the neighboring block beingan ALWIP-coded neighboring block, determine that a value of an intraprediction mode of the neighboring block is a default value, such as avalue corresponding to a planar mode. Video decoder 300 may include anintra prediction mode corresponding to the default value (e.g., theplanar mode) as one of the one or more MPMs. Video decoder 300 may thenuse one of the MPMs or another intra prediction mode to form theprediction block for the current block.

Video decoder 300 may then inverse scan the reproduced transformcoefficients (376), to create a block of quantized transformcoefficients. Video decoder 300 may then inverse quantize the transformcoefficients and apply one or more inverse transforms to the transformcoefficients to produce a residual block (378). Video decoder 300 maydecode the current block by combining the prediction block and theresidual block (380).

FIG. 19 is a flowchart illustrating an example method of coding videodata, in accordance with one or more techniques of this disclosure. Themethod of FIG. 19 may be performed by a video coder, such as videoencoder 200 or video decoder 300.

In the example of FIG. 19, the video coder may perform an MPM derivationprocess that derives one or more MPMs for a current block of the videodata (400). In some examples, intra-prediction unit 226 (FIG. 15) ofvideo encoder 200 performs the MPM derivation process. In some examples,intra-prediction unit 318 (FIG. 16) of video decoder 300 performs theMPM derivation process. In the example of FIG. 19, the current block isnot coded using ALWIP. The MPMs may include intra prediction modes and,in some examples, each of the MPMs is an intra prediction mode. Inexamples where the video coder is a video encoder (e.g., video encoder200), the video encoder may be included in a device (e.g., source device102) that includes a camera that captures a picture that includes thecurrent block.

Furthermore, in the example of FIG. 19, performing the MPM derivationprocess may include the video coder determining whether a neighboringblock of the current block is an ALWIP-coded neighboring block (402).The neighboring block may be an above neighboring block or a leftneighboring block of the current block. In some examples, the videocoder may store alwip_flags for blocks of the current picture and mayuse the stored alwip_flags of the neighboring block to determine whetherthe neighboring block is coded using ALWIP.

Based on the neighboring block being an ALWIP-coded neighboring block,the video coder may determine that a value of an intra prediction modeof the neighboring block is a default value (404). For instance, thevideo coder may determine (e.g., infer) the value of the intra mode ofthe neighboring block to be a particular value indicating the planarmode. In other words, the intra prediction mode corresponding to thedefault value may be the planar mode. In other examples, the intraprediction mode corresponding to the default value may be another intraprediction mode. The video coder may then include an intra predictionmode corresponding to the default value as one of the one or more MPMsfor the current block (406).

The video coder may code the current block based on one of the MPMs forthe current block (408). For instance, in examples where the video coderis a video encoder such as video encoder 200, the video encoder mayencode the current block based on one of the MPMs for the current block.In such examples, the video encoder may use the MPM to generate aprediction block for the current block. The video encoder may then usethe prediction block and samples of the current block to generateresidual data for the current block. The video encoder may then processthe residual data for the current block as described elsewhere in thisdisclosure, e.g., as with respect to FIG. 15. In examples where thevideo coder is a video decoder such as video decoder 300, the videodecoder may decode the current block based on one of the MPMs for thecurrent block. In such examples, the video decoder may use the MPM togenerate a prediction block for the current block. The video decoder maythen use the prediction block and residual data for the current block toreconstruct the current block. Furthermore, in some examples, a devicethat includes the video decoder may include a display that displays apicture that includes the current block.

FIG. 20 is a flowchart illustrating an example method of coding a chromablock, in accordance with one or more techniques of this disclosure. Inthe example of FIG. 20, a video coder (e.g., video encoder 200 or videodecoder 300) may be coding a chroma block using a DM mode.

Particularly, the video coder may determine whether a collocated lumablock is coded with ALWIP (450). The collocated luma block is collocatedwith the chroma block. Based on the collocated luma block being codedwith ALWIP, the video coder may determine that a value of an intraprediction mode of the collocated luma block is a default value, such asa value corresponding to the planar mode.

The video coder may then code the chroma block using an intra predictionmode corresponding to the default value (454). For instance, in exampleswhere the video coder is a video encoder such as video encoder 200, thevideo encoder may generate a prediction block for the chroma block usingthe intra prediction mode corresponding to the default value. The videoencoder may then use the prediction block and samples of the chromablock to generate residual data for the chroma block. The video encodermay then process the residual data for the chroma block as describedelsewhere in this disclosure, e.g., as with respect to FIG. 15. Inexamples where the video coder is a video decoder such as video decoder300, the video decoder may decode the chroma block based on the intraprediction mode corresponding to the default value. In such examples,the video decoder may use the intra prediction mode corresponding to thedefault value to generate a prediction block for the chroma block. Thevideo decoder may then use the prediction block and residual data forthe chroma block to reconstruct the chroma block. Furthermore, in someexamples, a device that includes the video decoder may include a displaythat displays a picture that includes the chroma block.

The following paragraphs provide a non-limiting set of examples that arein accordance with one or more techniques of this disclosure.

Example 1

A method of coding video data, the method including: determining acontext for an affine linear weighted intra prediction (ALWIP) syntaxelement that indicates whether a current block is coded with ALWIP,wherein an above neighbor block is determined to be unavailable fordetermining the context based on the above neighbor block being in adifferent coding tree unit (CTU) from the current block, the aboveneighbor block being an above neighbor of the current block; and codingthe ALWIP syntax element based on the context.

Example 2

A method of coding video data, the method including: coding a set ofblocks of the video data, wherein a constraint is imposed on the codingthat disables affine linear weighted intra prediction (ALWIP) for thoseones of the blocks that have a width less than a threshold width or aheight less than a threshold height.

Example 3

A method of coding video data, the method including: determining that aneighboring block for a current block of the video data is consideredunavailable based on the neighboring block being affine linear weightedintra prediction (ALWIP) coded and the neighboring block beingconsidered in a most-probable mode (MPM) derivation of a non-ALWIP codedblock of the video data; determining MPMs for the current block based onavailable neighboring blocks; and coding the current block based on oneof the MPMs.

Example 4

A method of coding video data, the method including: assigning a defaultvalue for a most-probable mode (MPM) derivation of an ALWIP block basedon a determination that a neighboring block for a current block of thevideo data is considered unavailable based on the neighboring blockbeing non-affine linear weighted intra prediction (ALWIP) coded and theneighboring block being used in a most-probable mode (MPM) derivation ofan ALWIP coded block of the video data; and using ALWIP to code thecurrent block.

Example 5

A method of coding video data, the method including: deriving amost-probable mode (MPM) list for affine linear weighted intraprediction (ALWIP) based on one or more blocks in a neighborhood of acurrent block of the video data; and using an MPM from the MPM list toperform ALWIP to code the current block.

Example 6

The method of example 5, wherein the one or more blocks in theneighborhood of the current block include a first neighboring block thatis above and adjacent to a top-right sample of the current block and asecond neighboring block that is left of and adjacent to a bottom-leftsample of the current block.

Example 7

A method including the methods of any combination of one or more ofexamples 1-6.

Example 8

The method of any of examples 1-7, wherein coding includes decoding.

Example 9

The method of any of examples 1-7, wherein coding includes encoding.

Example 10

A device for coding video data, the device including one or more meansfor performing the method of any of examples 1-9.

Example 11

The device of example 10, wherein the one or more means include one ormore processors implemented in circuitry.

Example 12

The device of any of examples 10 and 11, further including a memory tostore the video data.

Example 13

The device of any of examples 10-12, further including a displayconfigured to display decoded video data.

Example 14

The device of any of examples 10-13, wherein the device includes one ormore of a camera, a computer, a mobile device, a broadcast receiverdevice, or a set-top box.

Example 15

The device of any of examples 10-14, wherein the device includes a videodecoder.

Example 16

The device of any of examples 10-15, wherein the device includes a videoencoder.

Example 17

A computer-readable storage medium having stored thereon instructionsthat, when executed, cause one or more processors to perform the methodof any of examples 1-7.

Example 18

A device for coding video data, the device including means forperforming the methods of any of examples 1-7.

It is to be recognized that depending on the example, certain acts orevents of any of the techniques described herein can be performed in adifferent sequence, may be added, merged, or left out altogether (e.g.,not all described acts or events are necessary for the practice of thetechniques). Moreover, in certain examples, acts or events may beperformed concurrently, e.g., through multi-threaded processing,interrupt processing, or multiple processors, rather than sequentially.

In one or more examples, the functions described may be implemented inhardware, software, firmware, or any combination thereof. If implementedin software, the functions may be stored on or transmitted over as oneor more instructions or code on a computer-readable medium and executedby a hardware-based processing unit. Computer-readable media may includecomputer-readable storage media, which corresponds to a tangible mediumsuch as data storage media, or communication media including any mediumthat facilitates transfer of a computer program from one place toanother, e.g., according to a communication protocol. In this manner,computer-readable media generally may correspond to (1) tangiblecomputer-readable storage media which is non-transitory or (2) acommunication medium such as a signal or carrier wave. Data storagemedia may be any available media that can be accessed by one or morecomputers or one or more processors to retrieve instructions, codeand/or data structures for implementation of the techniques described inthis disclosure. A computer program product may include acomputer-readable medium.

By way of example, and not limitation, such computer-readable storagemedia can include RAM, ROM, EEPROM, CD-ROM or other optical diskstorage, magnetic disk storage, or other magnetic storage devices, flashmemory, or any other medium that can be used to store desired programcode in the form of instructions or data structures and that can beaccessed by a computer. Also, any connection is properly termed acomputer-readable medium. For example, if instructions are transmittedfrom a website, server, or other remote source using a coaxial cable,fiber optic cable, twisted pair, digital subscriber line (DSL), orwireless technologies such as infrared, radio, and microwave, then thecoaxial cable, fiber optic cable, twisted pair, DSL, or wirelesstechnologies such as infrared, radio, and microwave are included in thedefinition of medium. It should be understood, however, thatcomputer-readable storage media and data storage media do not includeconnections, carrier waves, signals, or other transitory media, but areinstead directed to non-transitory, tangible storage media. Disk anddisc, as used herein, includes compact disc (CD), laser disc, opticaldisc, digital versatile disc (DVD), floppy disk and Blu-ray disc, wheredisks usually reproduce data magnetically, while discs reproduce dataoptically with lasers. Combinations of the above should also be includedwithin the scope of computer-readable media.

Instructions may be executed by one or more processors, such as one ormore digital signal processors (DSPs), general purpose microprocessors,application specific integrated circuits (ASICs), field programmablegate arrays (FPGAs), or other equivalent integrated or discrete logiccircuitry. Accordingly, the terms “processor” and “processingcircuitry,” as used herein may refer to any of the foregoing structuresor any other structure suitable for implementation of the techniquesdescribed herein. In addition, in some aspects, the functionalitydescribed herein may be provided within dedicated hardware and/orsoftware modules configured for encoding and decoding, or incorporatedin a combined codec. Also, the techniques could be fully implemented inone or more circuits or logic elements.

The techniques of this disclosure may be implemented in a wide varietyof devices or apparatuses, including a wireless handset, an integratedcircuit (IC) or a set of ICs (e.g., a chip set). Various components,modules, or units are described in this disclosure to emphasizefunctional aspects of devices configured to perform the disclosedtechniques, but do not necessarily require realization by differenthardware units. Rather, as described above, various units may becombined in a codec hardware unit or provided by a collection ofinteroperative hardware units, including one or more processors asdescribed above, in conjunction with suitable software and/or firmware.

Various examples have been described. These and other examples arewithin the scope of the following claims.

What is claimed is:
 1. A method of coding video data, the methodcomprising: determining a context for an affine linear weighted intraprediction (ALWIP) syntax element, wherein the ALWIP syntax elementindicates that a current block of the video data is not coded withALWIP, wherein an above neighbor block is determined to be unavailablefor determining the context based on the above neighbor block being in adifferent coding tree unit (CTU) from the current block, the aboveneighbor block being an above neighbor of the current block, wherein thecontext for the ALWIP syntax element identifies probabilities of a binhaving particular values; coding the ALWIP syntax element based on thecontext performing a Most-Probable Mode (MPM) derivation process thatderives one or more MPMs for the current block, wherein performing theMPM derivation process comprises: determining that a neighboring blockof the current block is an ALWIP-coded neighboring block; and based onthe neighboring block being an ALWIP-coded neighboring block:determining that a value of an intra prediction mode of the neighboringblock is a default value; and including an intra prediction modecorresponding to the default value as one of the one or more MPMs; andcoding the current block based on one of the MPMs for the current block.2. The method of claim 1, wherein the intra prediction modecorresponding to the default value is a planar mode.
 3. The method ofclaim 1, wherein the current block is a first block, a second block ofthe video data is a chroma block coded with a Direct Mode (DM) mode, andthe method further comprises: determining whether a collocated lumablock is coded with ALWIP, the collocated luma block being collocatedwith the second block; and based on the collocated luma block beingcoded with ALWIP: determining that a value of an intra prediction modeof the collocated luma block is the default value; and coding the secondblock using an intra prediction mode corresponding to the default value.4. The method of claim 3, wherein the intra prediction modecorresponding to the default value is a planar mode.
 5. The method ofclaim 1, wherein a video coding standard imposes a constraint thatdisables ALWIP for blocks that have a width less than a threshold widthor a height less than a threshold height.
 6. The method of claim 5,wherein the threshold width is 8 and the threshold height is
 8. 7. Themethod of claim 1, wherein coding the current block comprises decodingthe current block.
 8. The method of claim 7, further comprisingdisplaying a picture that includes the current block.
 9. The method ofclaim 1, wherein coding the current block comprises encoding the currentblock.
 10. The method of claim 9, further comprising capturing a picturethat includes the current block.
 11. A device for coding video data, thedevice comprising: a memory to store the video data; and one or moreprocessors implemented in circuitry, the one or more processorsconfigured to: determine a context for an affine linear weighted intraprediction (ALWIP) syntax element, wherein the ALWIP syntax elementindicates that a current block of the video data is not coded withALWIP, wherein an above neighbor block is determined to be unavailablefor determining the context based on the above neighbor block being in adifferent coding tree unit (CTU) from the current block, the aboveneighbor block being an above neighbor of the current block, wherein thecontext for the ALWIP syntax element identifies probabilities of a binhaving particular values; code the ALWIP syntax element based on thecontext; perform a Most-Probable Mode (MPM) derivation process thatderives one or more MPMs for the current block, wherein the one or moreprocessors are configured to, as part of performing the MPM derivationprocess: determine that a neighboring block of the current block is anALWIP-coded neighboring block; and based on the neighboring block beingan ALWIP-coded neighboring block: determine that a value of an intraprediction mode of the neighboring block is a default value; and includean intra prediction mode corresponding to the default values as one ofthe one or more MPMs; and code the current block based on one of theMPMs for the current block.
 12. The device of claim 11, wherein theintra prediction mode corresponding to the default value is a planarmode.
 13. The device of claim 11, wherein the current block is a firstblock, a second block of the video data is a chroma block coded with aDirect Mode (DM) mode, and the one or more processors are furtherconfigured to: determine whether a collocated luma block is coded withALWIP, the collocated luma block being collocated with the second block;and based on the collocated luma block being coded with ALWIP: determinethat a value of an intra prediction mode of the collocated luma block isthe default value; and code the second block using an intra predictionmode corresponding to the default value.
 14. The device of claim 13,wherein the intra prediction mode corresponding to the default value isa planar mode.
 15. The device of claim 11, wherein a video codingstandard imposes a constraint that disables ALWIP for blocks that have awidth less than a threshold width or a height less than a thresholdheight.
 16. The device of claim 15, wherein the threshold width is 8 andthe threshold height is
 8. 17. The device of claim 11, wherein the oneor more processors are configured such that, as part of coding thecurrent block, the one or more processors decode the current block. 18.The device of claim 17, further comprising a display configured todisplay decoded video data.
 19. The device of claim 11, wherein the oneor more processors are configured such that, as part of coding thecurrent block, the one or more processors encode the current block. 20.The device of claim 11, wherein the device comprises one or more of acamera, a computer, a mobile device, a broadcast receiver device, or aset-top box.
 21. A device for coding video data, the device comprising:means for determining a context for an affine linear weighted intraprediction (ALWIP) syntax element, wherein the ALWIP syntax elementindicates that a current block of the video data is not coded withALWIP, wherein an above neighbor block is determined to be unavailablefor determining the context based on the above neighbor block being in adifferent coding tree unit (CTU) from the current block, the aboveneighbor block being an above neighbor of the current block, wherein thecontext for the ALWIP syntax element identifies probabilities of a binhaving particular values; means for coding the ALWIP syntax elementbased on the context means for performing a Most-Probable Mode (MPM)derivation process that derives one or more MPMs for the current block,wherein the means for performing the MPM derivation process comprises:means for determining that a neighboring block of the current block isan ALWIP-coded neighboring block; and means for determining, based onthe neighboring block being an ALWIP-coded neighboring block, that avalue of an intra prediction mode of the neighboring block is a defaultvalue and including an intra prediction mode corresponding to thedefault value as one of the one or more MPMs; and means for coding thecurrent block based on one of the MPMs for the current block.
 22. Thedevice of claim 21, wherein the intra prediction mode corresponding tothe default value is a planar mode.
 23. The device of claim 21, whereinthe current block is a first block, a second block of the video data isa chroma block coded with a Direct Mode (DM) mode, and the devicefurther comprises: means for determining whether a collocated luma blockis coded with ALWIP, the collocated luma block being collocated with thesecond block; means for determining, based on the collocated luma blockbeing coded with ALWIP, that a value of an intra prediction mode of thecollocated luma block is the default value; and means for coding thesecond block using an intra prediction mode corresponding to the defaultvalue.
 24. A non-transitory computer-readable storage medium havingstored thereon instructions that, when executed, cause one or moreprocessors to: determine a context for an affine linear weighted intraprediction (ALWIP) syntax element, wherein the ALWIP syntax elementindicates that a current block of video data is not coded with ALWIP,wherein an above neighbor block is determined to be unavailable fordetermining the context based on the above neighbor block being in adifferent coding tree unit (CTU) from the current block, the aboveneighbor block being an above neighbor of the current block, wherein thecontext for the ALWIP syntax element identifies probabilities of a binhaving particular values; code the ALWIP syntax element based on thecontext; perform a Most-Probable Mode (MPM) derivation process thatderives one or more MPMs for the current block, wherein the instructionsthat cause the one or more processors to perform the MPM derivationprocess comprise instructions that, when executed, cause the one or moreprocessors to: determine that a neighboring block of the current blockis an ALWIP-coded neighboring block; and based on the neighboring blockbeing an ALWIP-coded neighboring block: determine that a value of anintra prediction mode of the neighboring block is a default value; andinclude an intra prediction mode corresponding to the default value asone of the one or more MPMs; and code the current block based on one ofthe MPMs for the current block.
 25. The non-transitory computer-readablestorage medium of claim 24, wherein the intra prediction modecorresponding to the default value is a planar mode.
 26. Thenon-transitory computer-readable storage medium of claim 24, wherein thecurrent block is a first block, a second block of the video data is achroma block coded with a Direct Mode (DM) mode, and the instructions,when executed, further cause the one or more processors to: determinewhether a collocated luma block is coded with ALWIP, the collocated lumablock being collocated with the second block; and based on thecollocated luma block being coded with ALWIP: determine that a value ofan intra prediction mode of the collocated luma block is the defaultvalue; and code the second block using an intra prediction modecorresponding to the default value.